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MUM  FORD 

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EDITOR 


Ube  Iftural  Science  Series 

EDITED  BY  L.  H.  BAILEY 


THE   BREEDING   OF  ANIMALS 


i&ural  Science  Series 

EDITED  BY  L.  H.  BAILEY 

THE  SOIL.     Ring. 

THE  SPRAYING  OF  PLANTS.     Lodeman. 

MILK  AND  ITS  PRODUCTS.    Wing.   Enlarged  and  Revised. 

THE  FERTILITY  OF  THE  LAND.     Roberts. 

THE    PRINCIPLES    OF    FRUIT-GROWING.     Bailey.     20th 

Edition,  Revised. 
BUSH-FRUITS.     Card.     Revised. 
FERTILIZERS.     Voorhees.     Revised. 
THE  PRINCIPLES  OF  AGRICULTURE.    Bailey.     Revised. 
IRRIGATION  AND  DRAINAGE.     King. 
THE  FARMSTEAD.     Roberts. 
RURAL  WEALTH  AND  WELFARE.     Fairchild. 
THE  PRINCIPLES  OF  VEGETABLE-GARDENING.   Bailey. 
FARM  POULTRY.    Watson.    Enlarged  and  Revised. 
THE   FEEDING   OF   ANIMALS.      Jordan.       (Now   Rural 

Text-Book  Series  *) 

THE  FARMER'S  BUSINESS  HANDBOOK.     Roberts. 
THE  DISEASES  OF  ANIMALS.     Mayo. 
THE  HORSE.     Roberts. 
How  TO  CHOOSE  A  FARM.     Hunt. 
FORAGE.  CROPS.     Voorhees. 

BACTERIA  IN  RELATION  TO  COUNTRY  LIFE.     Lipman. 
THE  NURSERY-BOOK.     Bailey. 
PLANT-BREEDING.     Bailey  and  Gilbert.     Revised. 
THE  FORCING-BOOK.     Bailey. 

THE  PRUNING-BOOK.  Bailey.  (Now  Rural  Manual  Series.) 
FRUIT-GROWING  IN  ARID  REGIONS.  Paddock  and  Whipple. 
RURAL  HYGIENE.     Ogden. 
DRY-FARMING.     Widtsoe. 
LAW  FOR  THE  AMERICAN  FARMER.     Green. 
FARM  BOYS  AND  GIRLS.     McKeever. 
THE  TRAINING  AND  BREAKING  OF  HORSES.    Harper. 
SHEEP-FARMING  IN  NORTH  AMERICA.     Craig. 
COOPERATION  IN  AGRICULTURE.     Powell. 
THE  FARM  WOODLOT.     Cheyney  and  Wentling. 
HOUSEHOLD  INSECTS.     Herrick. 
CITRUS  FRUITS.     Coit. 
PRINCIPLES  OF  RURAL  CREDITS.     Morman. 
BEEKEEPING.     Phillips. 

SUBTROPICAL  VEGETABLE-GARDENING.     Rolfs. 
THE  POTATO.     Gilbert. 


THE 


BREEDING  OF  ANIMALS 


BY 


F.    B.    MUMFORD,   M.S. 

DEAN     OF     THE     COLLEGE     OF     AGRICULTURE     AND 

DIRECTOR    OF    THE    EXPERIMENT    STATION 

OF   THE    UNIVERSITY   OF   MISSOURI 


Wefo  ftafc 

THE  MACMILLAN  COMPANY 
1917 

All  rights  reserved 


s& 


COPYRIGHT,  1917, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  February,  1917. 


Xortoooti 

J.  8.  Gushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

THE  problems  of  the  animal-breeder  may  all  be 
grouped  under  the  three  subjects,  reproduction,  inherit- 
ance, development.  The  mere  multiplication  of  the 
species  is  now,  and  always  has  been,  the  major  work  of 
the  breeder  of  domestic  animals.  But  the  real  breeder 
is  not  only  concerned  with  the  production  of  mere 
numbers  of  animals  of  a  given  species  but  is  primarily 
interested  in  securing  animals  possessing  the  largest 
number  of  desirable  qualities  and  the  least  number  of 
qualities  undesirable  to  man. 

How  to  maintain  the  good  qualities  that  have  already 
appeared  in  an  individual,  and  how  to  cause  other  and 
better  qualities  to  become  dominant  in  future  indi- 
viduals of  the  same  species,  is  the  problem  of  inheritance 
that  chiefly  concerns  the  breeder  of  the  domestic  ani- 
mals. The  highest  attainments  in  the  breeder's  art 
have  come  only  to  those  who  have  had  a  good  knowl- 
edge of  the  principles  and  laws  of  heredity.  The  de- 
velopment of  animals  from  the  fertilization  of  the  egg 
to  maturity  and  their  proper  maintenance  throughout 
their  productive  lives  is  second  in  importance  only  to 
inheritance.  The  environment  of  the  animal,  including 
food,  climate,  and  exercise  of  functions,  determines  the 
degree  of  development  in  the  individual  animal.  The 
term  Development,  as  used  in  this  connection,  has  refer- 
ence to  the  unfolding  of  capabilities  that  have  come  to 
the  animal  through  inheritance. 


3721 68 


vi  PREFACE 

The  author  has  made  no  attempt  to  write  a  book  on 
genetics  or  evolution ;  but  the  principles  of  genetics  as 
they  apply  to  the  practice  of  animal-breeding  are  dis- 
cussed, in  accordance  with  the  conclusions  of  biologists. 
The  problems  of  the  animal-breeder  are  in  many  im- 
portant particulars  widely  different  from  those  of  the 
plant-breeder;  and  the  emphasis  has  been  placed  on 
those  principles  and  practices  that  belong  peculiarly  to 
the  province  of  the  animal-breeder,  while  not  neglecting 
the  lessons  and  illustrations  to  be  drawn  from  the  other 
field. 

It  has  been  the  purpose  to  make  a  practical  book 
which  shall  be  directly  useful  to  the  student  and  to  the 
breeder  of  animals,  and  the  lessons  and  examples  of 
which  can  be  applied  in  the  laboratory  and  on  the  farm. 


F.  B.  MUMFORD. 


COLUMBIA,  Mo. 

November,  1916. 


TABLE  OF  CONTENTS 


CHAPTER  I 

PAGES 

THE  CELL       ..........  1-15 

The  cell  theory,  1  ;  The  germ-cells,  2  ;  The  cell,  3  ;  Is 
the  cell  the  physiological  unit  ?  4  ;  The  structure  of  the 
cell,  5  ;  Protoplasm,  6  ;  The  nucleus,  7  ;  Growth  by  cell 
division,  8  ;  How  cells  divide,  9  ;  Prophase,  10  ;  Meta- 
phase,  11  ;  Anaphase,  12  ;  Telophase,  13;  The  germ-cells 
in  detail,  14  ;  The  ovum,  15  ;  The  spermatozoon,  16. 

CHAPTER  II 
REPRODUCTION        .........         16-51 

Asexual  reproduction,  17  ;  Sexual  reproduction,  18  ; 
The  reproductive  process,  19  ;  Oviparous  animals,  20  ; 
Primary  and  secondary  sexual  characters,  21  ;  The  re- 
productive organs  of  the  male,  22;  The  testicles,  23; 
Castration,  24  ;  The  reproductive  organs  of  the  female, 
25  ;  The  ovaries,  26  ;  The  Fallopian  tubes,  27  ;  The 
uterus,  28  ;  The  mammary  glands,  29  ;  Structure  of 
mammary  glands,  30  ;  Fertilization  of  the  ovum,  31  ; 
The  nature  of  fertilization,  32  ;  The  process  of  fertiliza- 
tion, 33  ;  The  chromosomes,  34  ;  Results  of  the  union  of 
egg  and  sperm,  35  ;  Changes  in  the  ovum,  36  ;  Changes 
in  the  spermatozoon,  37  ;  The  significance  of  reduction, 
38  ;  The  origin  of  the  germ-cells,  39  ;  Maturation  and 
reduction  in  the  female  (oogenesis),  40  ;  Reduction  in 
.  the  male  (spermatogenesis),  41  ;  The  period  of  the 
oestrum  or  heat,  42  ;  Artificial  insemination,  43  ;  Meth- 
ods of  artificial  insemination,  44  ;  Conditions  influenc- 
ing the  vitality  of  the  sperm-cells,  45  ;  Effect  of  too 
vii 


viii  TABLE  OF  CONTENTS 

PAGES 

frequent  breeding  on  the  sperm-cells,  46  ;  Vitality  of 
spermatozoa  within  the  female  generative  organs,  47  ; 
Effect  of  intoxication  of  the  male  parent  on  his  off- 
spring, 48  ;  Effect  of  lead  poisoning  on  the  male  germ- 
cells  as  indicated  by  the  offspring,  49. 

CHAPTER  III 

THE  BREEDING  SEASON 52-65 

Changed  conditions,  60 ;  Phases  of  the  breeding  sea- 
son, 51  ;  Procestram,  52  ;  CEstrum,  53  ;  Metoestrum,  54  ; 
Dicestrum,  55 ;  Puberty,  56 ;  Conditions  influencing 
puberty,  57  ;  The  O3strnm  and  lactation,  58  ;  Heat  dur- 
ing pregnancy,  59 ;  Superfcetation,  60 ;  Examples  of 
superfoetation,  61 ;  Recurrence  and  duration  of  the 
oestrum,  62  ;  Effect  of  ration  on  recurrence  of  oestrum,  63. 

CHAPTER   IV 
GESTATION  AND  LACTATION   .......         66-84 

Gestation :  Indications  of  pregnancy,  64  ;  Physical 
examination  for  pregnancy,  65  ;  The  period  of  gestation, 
66  ;  Causes  of  variation  in  length  of  gestation  period,  67 ; 
Incubation,  68 ;  Parturition,  69  ;  Normal  parturition  of 
the  domestic  animals,  70  ;  Mai-presentations,  71 ;  Normal 
presentations,  72  ;  Treatment  for  mal-presentation,  73. 

Lactation  :  The  mammary  glands,  74 ;  The  duration 
of  lactation,  75 ;  The  food  supply,  76  ;  Habit,  77  ;  He- 
redity, 78 ;  Exercise,  79 ;  Climate,  80 ;  Unusual  lacta- 
tion, 81. 

CHAPTER  V 

FERTILITY 85-112 

The  number  of  young  at  a  birth,  82  ;  Period  of  gesta- 
tion and  fertility,  83 ;  Fertility  and  the  frequency  of  the 
recurrence  of  the  oestrum,  84  ;  Fertility  and  gestation,  85  ; 
Duration  of  the  reproductive  period,  86;  Confinement 
and  fertility,  87  ;  The  fertility  of  domesticated  animals, 
88 ;  Age  and  fertility,  89 ;  Relation  of  age  to  fertility  in 


TABLE  OF  CONTENTS 


IX 


swine,  90 ;  Influence  of  age  of  sow  on  size  of  litter,  91 ;  Re- 
lation of  age  to  fertility  in  sheep,  92  ;  Influence  of  age 
of  ram  on  fertility  of  ewes,  93  ;  The  effect  of  the  age  of 
poultry  parents  on  the  offspring,  94  j  Age  and  fecundity, 
95 ;  Nutrition  and  fertility,  96  ;  Excessive  food  supply 
and  nutrition,  97  ;  Other  factors  affecting  fertility,  98  ; 
Relation  of  number  of  mammse  in  swine  to  fertility,  99  ; 
Twins,  100 ;  Characters  correlated  with  fertility,  101 ;  In- 
breeding and  fertility,  102  ;  Cross-breeding  and  fertility, 
103  ;  Unusual  fertility,  104  ;  Unusual  fertility  among 
horses,  105 ;  Unusual  fertility  among  cattle,  106 ;  Un- 
usual fertility  among  sheep,  107 ;  Unusual  fertility 
among  swine,  108  ;  Unusual  fertility  among  poultry,  109. 

CHAPTER   VI 
STERILITY       .......... 

The  causes  of  sterility,  110  ;  Causes  of  sterility  in  the 
male,  111  ;  Sterility  in  the  female,  112  ;  Closure  of  the 
cervix,  113  ;  Obstruction  of  Fallopian  tubes  resulting 
from  excessive  fatness,  114  ;  Other  causes  of  barrenness, 
115;  Sterility  from  fatty  degeneration,  116;  Sterility 
caused  by  abortion,  117  ;  Contagious  abortion  and  ste- 
rility, 118 ;  Treatment  for  contagious  abortion,  119  ; 
Diagnosis  of  contagious  abortion,  120  ;  The  complement 
fixation  test,  121  ;  Sterility  of  free-martins,  122. 


113-130 


CHAPTER   VII 
HEREDITY       .         .         .         .         .         .         .         . 

Development,  123 ;  Heredity  defined,  124  ;  Heredity 
and  variation  not  antagonistic,  125;  The  kinds  of  he- 
redity, 126 ;  Blending  inheritance,  127  ;  Alternative  in- 
heritance, 128  ;  Particulate  or  mosaic  inheritance,  129 ; 
Mendelian  inheritance,  130  ;  The  experiments  of  Men- 
.  del,  131 ;  The  law  of  dominance,  132  ;  The  law  of  seg- 
regation, 133 ;  Unit  characters,  134 ;  Gametic  purity, 
135 ;  Application  of  Mendel's  law,  136 ;  The  complexity 
of  animal  characters,  137  ;  The  inheritance  of  polled  and 
horned  character  in  cattle,  138 ;  Theory  of  pure  lines, 


131-156 


Xll 


TABLE  OF  CONTENTS 


CHAPTER  XII 

CROSS-BREEDING     ......... 

Permanent  and  temporary  results  of  cross-breeding, 
226 ;  Advantages  from  cross-breeding,  227  ;  Grading, 
228  ;  Cross-breeding  to  increase  fertility,  229  ;  Cross- 
breeding to  increase  size  and  restore  constitution,  230  ; 
Crossing  and  heredity,  231 ;  First  cross  and  improve- 
ment, 232  ;  Cross-breeding  as  a  cause  of  variation,  233  ; 
Crossing  species,  234 ;  Crossing  bison  and  cattle,  235  ; 
The  mule  hybrid,  236 ;  The  hinny  hybrid,  237  ;  Cross- 
ing the  horse  and  the  zebra,  238  ;  Crossing  cattle  and 
zebu,  239  ;  Sheep-goat  hybrid,  240. 


PAGES 

243-254 


CHAPTER   XIII 


DEVELOPMENT 


255-279 


Growth,  241 ;  The  growth  impulse,  242 ;  Factors  in- 
fluencing growth,  243  ;  Growth  and  food  supply,  244 ; 
Capacity  to  grow,  245  ;  Growth  and  the  cell,  246 ;  When 
the  growth  impulse  is  strongest,  247  ;  Development  of 
the  foetus,  248 ;  Heredity  and  foetal  development,  249  ; 
Birth  weight  of  lambs,  250  ;  Effect  of  protein  and  ash  in 
ration  on  foetal  development,  251 ;  High  calcium  rations 
for  pregnant  swine,  252 ;  Size  and  vigor  of  totus  as  in- 
fluenced by  corn  and  wheat  rations,  253  ;  The  perma- 
nent effect  of  retarded  growth,  254  ;  Early  stunting  and 
the  capacity  to  grow,  255  ;  Climate,  256  ;  The  age  factor 
in  animal-breeding,  267 ;  Premature  breeding  decreases 
size,  258  ;  Decreased  size  due  to  early  breeding  not  in- 
herited, 259 ;  Influence  of  early  pregnancy  on  the 
mother,  260 ;  Gestation  and  lactation  in  relation  to 
growth,  261 ;  The  Missouri  experiments,  262. 


CHAPTER   XIV 

THE  PRACTICE  OF  BREEDING 

Improvement  in  size,  263 ;  Improvement  in  function, 
264 ;  The  milking  function,  265  ;  Improvement  in  wool 
production,  266 ;  Improvement  in  tendency  to  lay  on  fat, 


280-303 


TABLE  OF  CONTENTS  xiii 

267  ;  Improvement  in  speed,  268  ;  Selection,  269 ;  Natu- 
ral selection,  270;  Methodical  selection,  271;  Im- 
portance of  selection  in  animal-breeding,  272 ;  Aids  to 
selection,  273 ;  The  real  results  of  selection  in  the  im- 
provement of  the  domestic  animals,  274;  Selection 
within  pure  lines,  275 ;  Vilmorin's  pure  line  wheat- 
breeding,  276  ;  Selection  most  useful  when  genetic  fac- 
tors are  not  pure,  277  ;  Pure  line  theory  not  opposed  to 
improvement  by  selection,  278 ;  Pedigree,  279 ;  Regis- 
tered breeding  animals,  280  ;  Registry  associations,  281 ; 
Community  breeding,  282  ;  Importance  of  numbers, 
283  ;  Selecting  the  best,  284 ;  Selecting  chance  varia- 
tions, 285 ;  The  Burbank  method,  286 ;  The  mendelian 
method,  287. 


ILLUSTRATIONS 


FIG.  PAGE 

1.  Cell  division.     Prophases.     After  Wilson      ....  9 

2.  Cell  division.     Later  phases.    After  Wilson          ...  11 

3.  The  ovarian  egg     .........  13 

4.  Human  spermatozoa      ........  14 

5.  Genital  organs  of  boar.    After  Ellenberger  ....  21 

6.  Sections  through  ovary  of  rat 25 

7.  Genital  organs  of  mare.     After  Ellenberger  .         .         .         .  26 

8.  Genital  organs  of  cow.     After  Ellenberger    ....  29 

9.  Genital  organs  "of  sow.     After  Ellenberger    ....  30 

10.  Genital  organs  of  bitch.    After  Ellenberger  .        .  32 

11.  Normal  presentation  in  mare          ...         ...  76 

12.  Posterior  presentation    .         .         .         .         .         .         .         .77 

13.  Abnormal  anterior  presentation 78 

14.  Abnormal  posterior  presentation 78 

15.  Abnormal  transverse  presentation 79 

16.  Diagram  illustrating  mendelian  inheritance  ....  140 

17.  Diagram  illustrating  mendelian  inheritance  ....  145 


PLATES 

PLATE  FACING  PAGE 

I.     Genital  organs  of  mare.     After  Ellenberger     ...      43 
II.     Superfoetation  in  mare 62 

III.  Upper :  A  mare  mule  that  secretes  milk  .        .        .        .84 
Lower:  A  Free-Martin  heifer 84 

IV.  Unusual  fertility  in  a  cow.     Triplet  calves        .         .         .     108 
V.     Normal,  heal  thy  uterus  of  sow  .        .        .        .        .-       .     118 

VI.     Uterus  of  sterile  sow          «        .        c  ,,;/••  •        •     H9 

xv 


XVI 


ILLUSTRATIONS 


PLATE  FACING   PAGE 

VII.     Upper:  Steer  fed  ration  not  restricted        .         .         .  162 

Lower  :  Steer  fed  greatly  restricted  ration          .        .  162 

VIII.     Upper  :  Steer  fed  ration  not  restricted        .        .        .  163 

Lower  :  Steer  fed  for  normal  growth  ....  163 

IX.     Upper :  Steer  fed  generously,  at  age  120  days     .         .  164 

Lower  :  Same  at  age  27  months 164 

X.     Upper  :  Dam  of  seven  mule  foals  followed  by  filly  foal  170 

Lower  :  Filly  foal  born  after  seven  mule  foals    .         .  170 

XL     Upper:  Eleventh  foal  following  ten  mule  foals  .         .  171 

Lower  :  Dam  of  ten  mule  foals  and  their  filly  foal      .  171 

XII.     Upper  :  Ninth  foal  following  eight  mule  foals     .         .172 

Lower  :  Foaled  after  eight  mule  foals  in  succession    .  172 

XIII.  Upper  :  Twelfth  foal  following  eleven  mule  foals        .  173 
Lower :  Mother  of  eleven  mule  foals  and  their  horse 

foal 173 

XIV.  Upper :  Close  in-breeding  of  fox  terrier       .        .         .  228 
Lower  :  Eighth  generation  of  intense  in-breeding        .  228 

XV.     In-bred  Berkshire 234 

XVI.     Cross-bred  Hereford- Aberdeen  Angus  steer         .         .247 

XVII.     Upper:  Half-blood  buffalo  (bison)  heifer   .        .        .  249 

Lower :  Cross-bred  buffalo-cattle  bulls        .         .         .  249 

XVIII.     Upper :  A  five-year-old  hinny     .        .        .         .     .  .  252 

Lower  :  Sheep-goat  hybrid 252 

XIX.     Effect  of  food  supply  on  development.     Side  view      .  257 

XX.     Same.     Front  view 257 

XXI.     Effect  of  starvation  on  capacity  to  grow      .        .        .  258 

XXII.     Recovery  from  starvation 259 

XXIII.  Upper  :  Cow  fed  corn  products 266 

Lower  :  Calf  from  cow  fed  corn  products   .         .        .  266 

XXIV.  Upper  :  Cow  fed  wheat  products         .        .         .        .267 
Lower  :  Calf  from  cow  fed  wheat  products         .        .  267 

XXV.     Permanent  effect  of  retarded  growth  .         .        .        .268 

XXVI.     Grace  Briggs  at  age  18  years 281 

XXVII.     Duchess  Skylark  Ormsby 282 

XXVIII.     Sophie  19th  of  Hood  Farm '     .  283 

XXIX.     Daughters  of  the  same  sire 286 

XXX.     Three  generations  showing  impressive  character  of 

original  dam          .......  287 

XXXI.     Result  of  using  a  pure-bred  sire  .         .  294 

XXXII.     Result  of  using  a  scrub  sire 295 


ACKNOWLEDGMENTS 

THE  author  is  indebted  to  R.  Pearl  for  Plate  IV,  to 
J.  W.  Connaway  for  Plates  V  and  VI,  to  P.  F.  Trow- 
bridge  for  Plates  VII,  VIII,  IX,  XXI,  XXII,  and  XXV, 
to  E.  A.  Trowbridge  for  Plate  XVI,  to  M.  Boyd  for 
Plate  XVII,  to  L.  Monsees  for  Plate  XVIII  upper,  to 
W.  J.  Spillman  for  Plate  XVIII  lower,  to  Hart  et  al. 
for  Plates  XXIII  and  XXIV,  to  C.  H.  Eckles  for 
Plates  XXVI,  XXIX,  and  XXX,  and  to  H.  Hackedorn 
for  Plates  XXXI  and  XXXII. 

Grateful  acknowledgment  is  made  to  all  these  persons 
for  their  valuable  assistance. 


THE  BREEDING  OF  ANIMALS 

CHAPTER  I 
THE  CELL 

THE  greatest  modern  contribution  to  the  science  of 
animal-breeding  was  the  formulation  of  the  so-called 
cell  theory.  This  fundamental  biological  generalization 
ranks  with  the  evolution  theory  in  importance  in  many 
respects;  it  has  given  a  definite  physical  basis  for  in- 
heritance. 

1.  The  cell  theory.  —  All  the  higher  forms  of  life  are 
made  up  of  cell  units,  and  from  these  all  parts  of  the 
body  are  constructed.  Although  various  in  form,  all 
living  cells  are  alike  in  having  within  a  mass  of  proto- 
plasm which  Huxley  called  the  "  physical  basis  of  life." 
In  the  simple  one-celled  forms  all  functions  are  found  in 
the  one  cell,  but  in  the  more  complex  higher  forms  a 
physiological  division  of  labor  results  in  the  distribution 
of  functions  among  the  cells.  "It  is  to  the  cell,"  says 
Verworn,1  "  that  the  study  of  every  bodily  function 
sooner  or  later  drives  us.  In  the  muscle  cell  lies  the 
problem  of  the  heart  beat  and  that  of  muscular  con- 
traction; in  the  gland  cell  reside  the  causes  of  secretion; 
in  the  epithelial  cell,  in  the  white  blood  cell,  lies  the 
problem  of  absorption  of  food,  and  the  secrets  of  the 

1  Wilson,  "  The  Cell,"  p.  6,  1911. 
B  1 


2  THE  BREEDING  OF  ANIMALS 

:'*.       ^\  N  ~*  2  j°*  "*>  -.J*  ""  *     *  <*,       * 

mind  are  hidden  in  the  ganglion  cell."  It  is  now  clearly 
apparent  that  the  great  questions  of  reproduction,  in- 
heritance and  development,  involving  as  they  do  the 
problems  of  embryology  and  evolution,  are  intricately 
bound  up  with  the  structure  and  functions  of  the  cell. 

2.  The  germ-cells.  —  The   heritage   of  the  species  is 
contained  within  the  germ-cell.     The  microscopic  egg  of 
the  female  carries  within  its  minute  structure  the  germ 
characters  of  all  the  maternal  ancestors.     The  germ-cell 
of  the  male,  the  spermatozoon,  holds  within  its  exceed- 
ingly minute  compass  the  sum  total  of  all  the  heritable 
characteristics  of  the  paternal  ancestors.     All  cells  are 
derived  from  other  cells.     Virchow's  claim  made  in  1855 
that  every  cell  must  have  been  formed  by  cell  division 
from  some  previously  formed  cell,  has  now  been  definitely 
established.     Not   only   does   growth   and   development 
take  place  by  cell  division  in  the  fertilized  egg-cell,  but 
the  egg-cell  itself  is  directly  derived  by  cell  division  from 
an  egg-cell  of  the  immediately  preceding  generation,  and 
so  on  indefinitely. 

3.  The  cell.  —  The  cell  is  a  mass  of  protoplasm  con- 
taining a  nucleus,  and  both  nucleus  and  protoplasm  arise 
through  division  of  the  corresponding  elements  of  a  pre- 
existing cell.1 

The  word  cell  is  derived  from  the  Greek  and  means  a 
hollow  chamber.  The  term  came  into  common  use  be- 
fore the  form  and  structure  of  the  cell  were  well  under- 
stood. The  cell-wall  which  is  characteristic  of  most 
cells  is  not  an  essential  part  of  its,  structure.  It  is  also 

1  Wilson,  "The  Cell  in  Development  and  Inheritance,"  p.  19, 
1906. 

Ley  dig,  "  Lehrbuch  der  Histologie,"  p.  9,  1857. 
Schultze,  "  Arch.  Anat.  u.  Phys.,"  p.  11,  1861. 


THE  CELL  3 

true  that  living  cells  are  never  hollow  chambers,  but  are 
filled  in  whole  or  in  part  by  a  colorless,  viscid,  semi-fluid 
substance,  protoplasm.  Many  cells  are  simply  masses 
of  protoplasm  lacking  entirely  any  kind  of  an  enclosing 
wall.  Lying  within  the  protoplasm  is  a  minute  body  of 
spherical  form  which  is  the  cell  nucleus.  These  two, 
the  protoplasm  and  the  nucleus,  are  of  universal  occur- 
rence and  are  the  essential  components  of  a  living  cell. 

4.  Is  the  cell  the  physiological  unit  ?  —  A  study  of  the 
form  and  function  of  the  cell  leads  to  the  inevitable 
conclusion  that  in  a  very  real  sense  the  cell  is  the  mor- 
phological unit  of  the  organism.  In  its  physiological 
relations  to  the  cells  of  the  body  as  a  whole,  however, 
it  is  not  to  be  regarded  as  an  independent  unit  but  rather 
as  a  localized  center  of  bodily  activities.  The  individual 
cell  in  a  multicellular  body  is  influenced,  sometimes  in 
a  marked  degree,  by  the  surrounding  cells.  The  most 
fundamental  problem  in  growth  and  development  of 
animals  is  what  and  how  much  influence  do  the  body- 
cells  of  one  group  have  over  the  cells  of  another  group. 
Is  there  a  physiological  connection  between  adjoining 
cells?  Can  a  group  of  cells  forming  a  so-called  system 
like  the  reproductive  system  in  the  animal  body  be  in- 
fluenced by  the  soma  or  body-cells  ?  If  influenced  at  all, 
can  such  influence  have  any  effect  upon  the  germ  plasm 
in  the  nucleus  of  the  germ-cell  ?  Is  it  probable  that  the 
germ  characters  may  be  changed  by  these  influences  so 
that  the  offspring  of  the  parent  bodies  where  these  in- 
fluences have  been  at  work,  will  correspond  in  any  way 
to  the  changes  occurring  in  the  parent  body?  In  other 
words,  are  acquired  habits  transmitted  ?  It  is  to  be  re- 
gretted that  the  microscopic  study  of  the  cell  has  thrown 
little  light  upon  this  fundamental  question.  As  indicated 


4  THE  BREEDING  OF  ANIMALS 

above,  the  cell  in  the  animal  body  is  in  more  or  less  close 
physiological  relation  with  the  other  cells  of  the  body, 
but  these  relationships  and  their  bearings  upon  the 
fundamental  facts  of  biology  have  not  yet  been  clearly 
determined. 

5.  The  structure  of  the  cell.  —  The  cell  contains  a 
cell-body  and  the  nucleus.     The  cell-body  is  all  that 
portion  of  the  protoplasm  not  contained  in  the  nucleus. 
The  cell  in  its  simplest  form  is  a  rounded  mass  of  proto- 
plasm.    This  type  is  found  generally  in  one-celled  forms 
and  is  the  characteristic  form  of  the  egg-cell  of  the  higher 
animals.     The  fact  that  the  form  of  cells  in  the  higher 
plants  and  animals  is  not  always  rounded  spherical  is 
due  to  unequal  pressure  and  the  movement  of  the  cells 
comprising  the  body. 

The  nucleus  is  a  definite,  clearly-marked  body  existing 
within  the  protoplasmic  contents  of  the  living  cell,  and 
its  relation  to  growth,  reproduction  and  heredity  have 
given  it  a  commanding  position  in  the  study  of  modern 
biological  problems.  Other  bodies  are  often  found  in 
the  cell,  such  as  food  granules,  products  of  excretion, 
fat  globules  and  crystals.  None  of  these  plays  an  active 
part  in  the  metabolism  of  the  cell  and  may  be  regarded 
as  accidental  or  at  least  subsidiary  to  the  major  role 
played  by  the  protoplasm  itself.  Another  body  generally 
found  in  the  cell  is  the  centrosome  which  is  concerned 
with  the  mechanism  of  cell  division.  The  cell-wall  is 
generally  present  in  the  higher  forms  of  plant  and  animal 
life  and  consists  of  a  membrane  which  is  usually  lifeless. 

6.  Protoplasm.  —  The  protoplasm  is  universally  present 
in  every  living  cell.     It  is  the  most  fundamentally  impor- 
tant life  substance.     Huxley  aptly  designated  protoplasm 
as  "  the  physical  basis  of  life."     It  is  not  to  be  regarded 


THE  CELL  5 

as  being  a  definite  chemical  substance,  as  its  composition 
changes.  It  is  a  viscid,  colorless,  semifluid  material 
having  a  higher  index  of  refraction  than  water,  and  hence 
appears  brighter.  It  was  called  slime  by  Schleiden. 
The  protoplasm  of  the  cell  has  a  definite  structural 
arrangement  appearing  as  a  meshwork,  or  reticulum,  and 
a  ground  substance,  or  cell-sap,  filling  the  intervening 
spaces.  In  addition  to  these  two  definite  substances 
there  are  present  in  the  protoplasm  minute  granules 
or  microsomes  which  are  distributed  regularly  or  irregu- 
larly along  the  lines  of  the  meshwork.  While  other 
materials  are  often  found  in  the  protoplasm,  the  above 
materials  are  regarded  as  the  essential  elements  of  pri- 
mary importance  in  the  activities  of  the  cell. 

7.  The  nucleus.  —  The  nucleus  is  the  center  of  the 
constructive  activities  of  the  cell.  When  the  nucleus  is 
destroyed,  those  processes  which  result  in  the  growth 
and  development  of  the  organism  can  no  longer  take 
place.  Only  destructive  activities  are  possible  in  a  cell 
devoid  of  a  nucleus,  and  these  can  go  forward  for  only  a 
limited  time.  "  The  nucleus  is  generally  regarded,"  says 
Wilson,  "  as  a  controlling  center  of  cell  activity,  and  hence 
a  primary  factor  in  growth,  development  and  the  trans- 
mission of  specific  qualities  from  cell  to  cell,  and  from 
one  generation  to  another." l  Growth  is  the  result 
of  cell  division,  and  the  impetus  for  cell  division  appears 
to  come  from  the  nucleus.  The  essential  fact  in  cell 
division  is  that  a  portion  of  the  nuclear  material  of  the 
parent  cell  shall  pass  into  the  new  cell.  The  new  cell 
in  its  turn  becomes  a  parent  cell,  and  so  the  process  of 
growth  continues.  The  nucleus  is  typically  spherical 
and  moves  freely  within  the  cell.  It  exhibits  two  distinct 

1  Wilson,  "The  Cell  in  Development  and  Inheritance,"  p.  30. 


6  THE  BREEDING  OF  ANIMALS 

phases  which  result  from  the  varying  degrees  of  activity 
present  in  the  nuclear  substance.  One  phase  may  be 
designated  as  the  vegetative  or  quiescent  stage  and  the 
other  the  active  stage  which  is  characteristic  of  that 
period  in  the  development  of  the  nucleus  when  the  many 
complicated  and  significant  changes  occur  which  result 
in  cell  division  and  in  reproduction. 

The  typical  nucleus  during  the  vegetative  stage  pos- 
sesses certain  distinct  structural  forms  which  are  con- 
cerned in  the  many  important  nuclear  activities :  (1) 
The  nuclear  wall  which  encloses  the  nucleus  and  dif- 
ferentiates the  nucleus  from  the  cell-body;  (2)  The 
reticulum,  which  is  the  primary  factor  in  nuclear  activities, 
and  appearing  as  an  irregular  network.  The  reticulum 
in  turn  comprises  two  structures,  the  linin  and  the  chro- 
matin.  The  latter  is  undoubtedly  the  most  fundamentally 
important  organic  substance  concerned  with  the  growth, 
development  and  inheritance  of  plants  and  animals. 
It  is  apparently  the  only  or  chief  material  which  is  trans- 
mitted from  the  parent  cell  to  the  new  or  daughter  'cell 
by  division,  and  from  it  all  nuclear  substance  may  be  re- 
formed. The  word  chromatin  is  given  to  this  material 
because  it  becomes  deeply  stained  upon  the  addition  of 
certain  well-known  reagents.  The  chromatin  may  appear 
in  the  cell  in  scattered  granules,  varying  in  size  and  form, 
or  in  a  single  deeply  staining  mass,  but  more  often  the 
arrangement  of  the  chromatin  in  the  nucleus  resembles 
a  network  which  is  closely  associated  with  the  clearly 
differentiated  linin.  (3)  The  nucleoli  are  generally  but 
not  always  present,  and  their  nature  and  functions  are 
not  well  understood.  By  some  authorities  the  nucleoli 
are  the  by-products  of  the  activities  going  on  in  the 
nucleus.  (4)  The  ground  substance  is  a  fluid  filling 


THE  CELL  7 

the  chromatin  network  and  is  not  stained  by  ordinary 
reagents. 

8.  Growth  by  cell  division.  —  How  does  growth  take 
place  in  a  living  organism?  What  are  the  primary 
factors  concerned  in  the  increase  in  size?  What  changes 
in  the  organism  result  in  the  progressive  development 
of  the  many  useful  qualities  found  in  the  improved  types 
of  the  domestic  animals?  How  does  a.  microscopic  egg- 
cell  develop  into  a  mature  and  highly  organized  animal 
possessing  countless  cells  of  many  different  forms  and 
exercising  various  and  important  functions?  A  still 
more  fundamental  problem,  if  possible,  is,  how  are  the 
qualities  of  an  individual  transmitted  from  parent  to 
offspring  ?  What  is  the  physical  basis  of  heredity  and 
what  are  the  elements  concerned  in  a  study  of  inheritance  ? 

Many  of  these  questions  are  answered  by  a  study  of 
the  cell  and  specifically  by  a  study  of  cell  division.  The 
entire  tissue  structure  of  the  animal  body  arises  by  re- 
peated division  from  the  germ-cell.  The  germ-cell  itself 
is  the  result  of  the  division  of  a  cell  which  formed 
a  part  of  the  body  of  the  parent.  Thus  it  is  that  the 
germ  substance  carrying  the  hereditary  material  is 
separated  from  the  parent  body  by  cell  division.  The 
fertilized  egg  by  continued  cell  division  passes  on  to  every 
cell  in  the  body  a  portion  of  its  own  substance.  The 
process  of  cell  division  must  therefore  be  regarded  as  a 
great  fundamental  fact  in  the  growth  and  development 
of  plants  and  animals  as  well  as  one  of  the  most  significant 
and  primary  facts  in  the  transmission  of  qualities  from 
parent  to  offspring. 

Growth  occurs  as  the  result  of  continued  cell  division 
rather  than  by  any  material  increase  in  the  size  of  exist- 
ing cells. 


8  THE  BREEDING  OF  ANIMALS 

9.  How  cells  divide.  —  All  cells  do  not  divide  in  the 
same  manner,  but  the  most  typical  process  is  known  as 
indirect  division  or  mitosis,  and  this  will  be  here  described. 
We  have  seen  that  the  nucleus  contains  within  its  minute 
compass  the  active  material  which  stimulates  the  cell 
to   various   activities   and   determines   its   physiological 
destiny.     If  further  evidence  was  needed  on  this  point, 
it  would  be  found  in  the  remarkable  and  interesting  trans- 
formations which  take  place  within  the  nucleus  before 
and  during  the  process  of  cell  division. 

The  cell  first  passes  through  a  vegetative  or  quiescent 
stage*,  and  this  is  followed  by  a  period  of  activity  finally 
resulting  in  the  formation  of  two  cells  from  the  original 
parent  cell.  Various  clearly  marked  stages  or  phases 
are  distinguishable  in  this  process  which  have  been  accu- 
rately described  by  Wilson.  The  phases  observed  are 
for  convenience  named :  (1)  prophase,  (2)  metaphase, 
(3)  anaphase,  and  (4)  telophase. 

10.  Prophase  (Fig.  1).  —  In  the  vegetative  stage  the 
chromatin  of  the  nucleus  exists  in  the  form  of  a  network. 
Generally  during  the  prophase  the  chromatin  loses  its 
net-like  arrangement  and  assumes  the  form  of  a  skein 
like  thread  known  as  the  spireme.     During  this  stage 
the  spireme  thread  stains  intensely  and  is  fine  and  closely 
convoluted.     It  gradually  becomes  thicker  and  the  con- 
volutions become  more  open,  giving  rise  to  the  "  open 
spireme."     Gradually  the  spireme  breaks  up  into  a  num- 
ber of  definite  straight  or  curved  rods  known  as  chromo- 
somes.    It  is  usual  for  the  wall  of  the  nucleus  to  disappear 
during  this  phase,  and  the  chromosomes  then  lie  naked 
in  the  protoplasm  of  the  cell.     It  is  a  significant  fact  that 
every  plant  and  animal  possesses  a  characteristic  number 
of  chromosomes  and  that  this  number  is  always  even. 


FIG.  1.  —  Cell  division.  Diagram  showing  typical  pro  phases  in  cell 
division.  A,  Vegetative  or  resting  stage  showing  nucleus.  B,  The 
spireme  thread.  C,  Preparation  for  division.  D,  Formation  of  chro- 
mosomes. E,  Gradual  fading  of  nuclear  membrane.  F,  Chromosomes 
in  equatorial  plate  ready  for  division. 

9 


10  THE  BREEDING  OF  ANIMALS 

In  the  ox  and  in  man  the  number  is  sixteen.  The  fact 
that  the  number  of  chromosomes  is  even  in  all  species  is 
due  to  the  fact  that  during  the  processes  of  fertilization 
one-half  the  chromosomes  are  derived  from  the  female 
and  one-half  from  the  male  parent. 

After  the  breaking  up  of  the  spireme  thread  into  a 
definite  number  of  chromosomes,  there  is  formed  in  the 
cell  the  so-called  amphiaster.  The  development  and 
activities  of  this  interesting  structure  seem  to  be  for  the 
purpose  of  arranging  the  chromosomes  in  position  for 
division.  All  the  processes  concerned  in  the  prophases 
are  preparatory  to  the  final  division,  and  ultimate  dis- 
tribution of  chromatin  to  the  new  cell. 

11.  Metaphase.  —  Each  chromosome  now  splits  into 
two  exactly  equal  halves  and  the  two  new  groups  move 
to  opposite  sides  of  the  cell.  The  chromosomes  divide 
lengthwise,  and  by  so  doing  there  results  an  accurate 
division  of  the  chromatin  into  two  precisely  equivalent 
portions.  Each  portion  eventually  becomes  the  nucleus 
of  one  of  the  two  new  daughter  cells  which  result  from 
this  division.  The  most  fundamentally  important  fact 
about  this  division  of  the  chromatin  is  that  it  is  a  qualita- 
tive as  well  as  a  quantitative  division.  There  is  much  evi- 
dence to  show  that  the  spireme  thread  (and,  therefore, 
the  chromosomes)  is  composed  of  granules  or  units 
throughout  its  length,  and  each  of  these  units  represents 
a  definite  character  or  set  of  characters  in  the  individual. 
It  follows  that  when  a  lengthwise  division  occurs,  these 
units  are  divided  and  a  portion  of  each  is  passed  on  to  the 
daughter  cells  (Fig.  2). 

The  arrangement  of  the  chromatin  in  the  spireme,  its 
breaking  up  into  chromosomes,  and  the  splitting  of  the 
latter  into  halves  are  all  directed  toward  the  accurate 


THE  CELL 


11 


H 


FIG.  2.  —  Diagram  of  later  phases  of  cell  division.  G,  Splitting  of 
the  chromosomes.  H,  Daughter  chromosomes  diverging  to  form  new 
cells.  7,  Chromosomes  grouped  in  daughter  nuclei,  final  changes  before 
complete  division.  J,  The  two  new  cells. 


division  of  the  smaller  chromatin  granule  (chromo- 
mere  or  id  as  designated  by  Weismann).  In  this  process, 
therefore,  we  have  a  reasonable  physical  basis  for  a  better 
understanding  of  the  transmission  of  characters  from 


12  THE  BREEDING  OF  ANIMALS 

parent  cell  to  daughter  cell  and  thus  from  parent  to  off- 
spring. 

12.  Anaphase.  —  The  essential  step  in  the  anaphase 
is  the  separation  of  the  two  groups  of  chromosomes  which 
were  derived  from  the  splitting  of  the  chromosomes  of 
the  parent  cell.     These  pass  to  opposite  sides  of  the  cell, 
and  in  many  forms  these  new  groups  begin  at  once  to 
assume  the  appearance  of  the  original  nuclear  material. 

13.  Telophase.  —  Complete    division    of    the    cell    is 
finally  accomplished  by  constriction  of  the  parent  cell- 
walls  and  the  formation  of  a  new  membrane  which  encloses 
the  two  daughter  nuclei  each  in  its  own  cell.     The  two 
groups  of  chromosomes  derived  from  the  parent  nucleus 
are  rearranged  and  become  the  nuclei  of  the  new  daughter 
cells  which  in  their  turn  may  pass  through  all  the  stages 
described  above. 

The  essential  steps,  then,  in  cell  division  are :  (1)  The 
formation  of  the  spireme  thread  from  the  chromatin 
and  its  division  into  chromosomes;  (2)  The  splitting  of 
the  chromosomes  through  the  middle  longitudinally; 
(3)  The  movement  of  the  divided  portions  of  the  chromo- 
somes to  the  new  or  daughter  cells. 

14.  The  germ-cells  in  detail.  —  In  all  the  higher  forms 
of  animals,  reproduction  is  accomplished  by  the  forma- 
tion of  special  reproductive  cells  called  the  germ-cells. 
The  germ-cells  are  the  product  of  the  reproductive  group 
of  cells  and  are  endowed  with  peculiar  powers  not  gen- 
erally possessed  by  the  soma-  or  body-cells.    Weismann 
divided  the  cells  of  the  body  into  two  very  clearly  marked 
and  distinct  groups,  the  soma-  or  body-cells  and  the  germ- 
cells.    The  soma-cells  are  primarily  concerned  with  the 
individual  life  of  the  animal,  while  the  germ-cells  are 
destined  solely  for  the  purpose  of  reproduction.     The 


THE  CELL  13 

germ-cells  have  no  important  relation  to  the  functional 
activities  which  are  especially  concerned  with  the  indi- 
vidual existence  of  the  animal.  They  are  clearly  in- 
tended for  ultimate  separation  from  the  individual  and 
destined  to  provide  for  the  continuance  of  the  species. 
In  some  lower  forms  of  life,  the  body-cells  and  germ-cells 
are  not  so  clearly  separated,  but  in  the  domestic  animals 
such  differentiation  is  characteristic.  The  male  germ-cell 
is  called  the  spermatozoon  or  sperm-cell,  and  the  female 
germ-cell  the  egg  or  ovum. 

15.  The  ovum.  —  The  germ-cell  of  the  female  is  the 
egg  or  ovum  (Fig.  3).  It  is  one  of  the  largest  cells  in  the 
animal  body.  It  is  spheroidal  in 

,      •  1 

shape  and  contains  a  nucleus  or 
germinal  vesicle  and  within  the 
nucleus  a  nucleolus  or  germinal 
spot  and  a  large  amount  of  pro- 
toplasm (cytoplasm)  surrounding  6 
the  nucleus.  In  the  protoplasm 
are  often  distributed  numerous 
masses  of  material  or  yolk,  the 

function    of    which    Seems    to    be  FIG.    3. —  The     ovarian 

chiefly  to  nourish  the  fertilized  eff sm  A  nucleus ;  S'cyt0' 
egg-cell.  The  nucleus  of  the 

ovum  during  the  quiescent  stage  lies  near  the  center  of 
the  cell,  but  gradually  moves  toward  the  cell-wall  as  the 
egg  becomes  more  mature.  During  the  final  stages  in  the 
development  of  the  egg,  the  nucleus  loses  a  large  part  of 
its  chromatin.  This  process  is  called  maturation  and  re- 
sults .ultimately  in  reducing  the  number  of  chromosomes  to 
one-half  the  number  characteristic  of  the  species.  This 
process  is  preparatory  to  the  fertilization  of  the  egg  by 
the  spermatozoon.  During  fertilization,  the  chromo- 


14 


THE  BREEDING  OF  ANIMALS 


somes  of  the  egg-cell  unite  with  those  of  the  sperm-cell 
and  a  new  nucleus  is  thus  formed  which  becomes  the 
active  center  of  the  new  daughter  cell. 

16.   The  spermatozoon. — The  male  germ-cell  or  sper- 
matozoon is  exceedingly  minute  and  its  investigation  cor- 


FIG.  4.  —  Human  spermatozoa  (greatly  magnified),  a,  acrosome; 
6,  nucleus ;  c,  end  knob ;  d,  middle  piece ;  e,  tail ;  /,  end  piece ;  g,  axial 
filament. 

respondingly  difficult.  Although  early  discovered,  its 
significance  was  not  clearly  determined  until  1865  when 
Schweigger-Seidel  and  St.  George  discovered  that  the 
sperm  was  a  cell  and  contained  a  nucleus,  cytoplasm  and 
all  the  essential  "elements  of  a  perfect  cell.  The  function 
of  the  sperm-cell  is  to  fertilize  the  egg  and  thus  provide 


THE  CELL  15 

for  the  reproduction  of  the  species.  The  spermatozoon 
in  its  gross  anatomy  has  the  semblance  of  a  very  minute 
tadpole  swimming  freely  about  in  liquids.  It  has  a 
distinct  head  piece  and  a  long  slender  tail  piece  or  cilium. 
(See  Fig.  4.)  When  closely  examined,  the  sperm-cell 
exhibits  all  the  essential  characteristics  of  a  typical  cell, 
with  a  nucleus,  cytoplasm  and  a  cell-wall.  This  cell  is 
so  small  that  in  some  forms  it  is  but  iooVoo  of  the  size 
of  the  egg-cell.  The  nucleus  occupies  almost  the  entire 
space  available  in  the  head  piece,  being  surrounded  by 
a  very  thin  layer  of  cytoplasm  between  it  and  the  cell- 
wall.  The  tail  of  the  sperm-cell  is  joined  to  the  head 
piece  by  the  middle  piece.  It  is  of  cytoplasmic  origin 
and  possesses  the  power  of  motion.  This  ability  to  propel 
itself  forward  in  liquid  media  seems  to  be  in  a  way  an 
insurance  that  the  sperm-cell  will  ultimately  approach 
the  egg-cell  for  the  purpose  of  fertilization. 

The  power  of  motion  is  retained  by  the  spermatozoon 
for  a  considerable  time  under  favorable  conditions  of 
warmth  and  moisture.  After  the  sperm  enters  the  egg, 
it  loses  the  power  of  motion  and  the  tail  piece  is  absorbed. 

The  essential  portions  of  the  sperm  which  are  concerned 
in  the  process  of  fertilization  are  the  nucleus  and  the 
middle  piece.  Other  structures  which  are  accessory  to 
these  are  the  apex  by  which  the  sperm  attaches  itself 
to  the  ovum  and  the  tail  whose  functions  have  already 
been  described. 


CHAPTER  II 
REPRODUCTION 

THE  value  of  a  breeding  animal  is  measured  by  its 
own  individual  character,  its  ability  to  transmit  desir- 
able characters  to  its  offspring,  and  by  its  prolificacy.  Of 
two  animals  of  equal  individuality  and  inheritance,  the 
one  capable  of  producing  numerous  and  vigorous  offspring 
will  be  the  more  valuable.  The  subject  of  reproduction 
in  animal-breeding  is  therefore  of  great  importance  and 
second  only  to  inheritance  in  estimating  animal  values. 

Two  methods  of  reproduction  are  common  among 
plants  and  animals,  asexual  and  sexual.  These  differ 
greatly  in  form  and  method  but  accomplish  the  same 
ultimate  result,  which  is  the  continuance  of  the  race. 

17.  Asexual  reproduction.  —  The  asexual  method  of 
reproduction  is  common  among  the  simplest  forms  of 
plant  and  animal  life.  It  is  a  process  of  cell  division 
or  fission  which  varies  in  different  forms,  but  in  its  most 
elementary  manifestations  it  is  simple  cell  division.  In 
unicellular  forms  the  cytoplasm  of  the  cell  and  the  nucleus 
divide  into  two  equal  parts  and  each  half  becomes  a 
perfect  new  individual.  Each  new  cell  increases  in  bulk 
by  the  absorption  of  food  and  in  turn  becomes  a  parent 
cell  and  reproduces  by  division  as  before.  A  similar 
form  of  reproduction  is  found  in  the  developing  embryo 
of  mammals  and  of  the  other  body-cells.  The  tissues  of 

16 


REPRODUCTION  17 

the  body  thus  formed  cannot,  however,  continue  to  divide 
indefinitely,  but  sooner  or  later  reach  their  full  develop- 
ment and  do  not  thereafter  increase  in  bulk  by  further 
division. 

18.  Sexual  reproduction.  —  Reproduction  in  the  higher 
forms  of  organic  life  is  a  complicated  process  and  is  ac- 
complished by  the  activities  of  a  special  group  of  cells 
which  is  called  the  reproductive  or  generative  system. 
These  germ-cells  are  highly  specialized,  and  their  develop- 
ment and  functions  divide  the  individuals  of  a  species 
into  two  sexes,  male  and  female.     The  two  sexes  differ 
widely  in  form  and  characters,  but  particularly  in  respect 
to   their   physiological   relations   to   reproduction.     The 
product  of  the  male  germ-cells  is  the  spermatozoon,  an 
exceedingly  small  cell  but  carrying  in  its  minute  substance 
the  inherited  potentialities  of  its  ancestors.     The  female 
germ-cell  or  ovum  similarly  derived  from  the  female  is 
much  larger,  but  also  carries  the  germ  substance  which 
later,  after  fertilization  by  the  spermatozoon  and  under 
proper  conditions,  will  become  a  new  individual. 

19.  The   reproductive   process.  —  The   essential   fact 
in  the  reproductive  processes  of  all  vertebrate  animals 
is  the  formation  of  an  egg  or  ovum  by  the  female  and  of  a 
fecundating  fluid  containing  the  spermatozoon  or  sperm- 
cell  by  the  male.     The  union  of  the  two  germ-cells  is  the 
first  step  in  the  independent  existence  of  the  new  indi- 
vidual.    The  conjugation  of  the  egg  and  spermatozoon 
sets  in  motion  a  series  of  events  which,  whether  viewed 
from  the  standpoint  of  racial  significance  or  of  biological 
interest,  has  no  parallel  in  the  whole  realm  of  biology. 
Upon  the  successful  development  of  the  fertilized  egg- 
cell  depends  the  future  of  the  species.     The  union  of  the 
egg  and  spermatozoon  takes  place  in  some  forms  outside 


18  THE  BREEDING  OF  ANIMALS 

the  body  of  the  female.  In  fishes,  the  spawn  con- 
taining the  eggs  is  deposited  in  the  water  by  the  female, 
and  the  fertilizing  fluid  of  the  male  containing  the  sper- 
matozoa is  also  deposited  in  the  water  on  or  near  the  female 
spawn.  In  all  higher  animals,  including  the  domestic 
animals,  the  fecundating  fluid  of  the  male  reaches  the 
egg  inside  the  body  of  the  female,  and  the  process  of  ferti- 
lizing the  egg  is  accomplished  within  the  generative  organs 
of  the  female. 

20.  Oviparous  animals.  —  In  some  species  of  animals, 
including  birds,  fishes,  most  reptiles,  and  nearly  all 
invertebrates,  the  eggs  are  deposited  outside  the  body 
either  before  or  after  fertilization.  In  the  bird  family, 
which  includes  all  the  domestic  fowls,  the  egg  is  fertilized 
inside  the  body  of  the  mother,  where  it  undergoes  some 
slight  development  before  being  eventually  deposited  or 
laid  outside  the  body  of  the  female.  Animals  of  this 
class  are  called  oviparous,  to  distinguish  them  from  vivip- 
arous forms  which  bring  forth  their  young  alive.  The 
future  development  of  the  egg  deposited  by  oviparous 
animals  is  dependent  upon  its  being  supplied  with  favor- 
able conditions  of  heat  and  moisture.  This  period  of 
development  outside  the  body  is  called  the  period  of 
incubation  and  is,  in  many  ways,  similar  to  the  period 
of  gestation  in  viviparous  animals.  Animals  in  which 
the  fertilized  egg  develops  inside  the  body  are  called  vivip- 
arous, and  this  development  proceeds  to  a  point  where 
the  young  animal  is,  in  the  main,  able  to  carry  on  a  sepa- 
rate and  independent  existence.  The  period  of  growth 
inside  the  body  of  the  mother  in  mammalian  animals  is 
called  the  period  of  gestation,  and  during  this  period 
the  developing  embryo  is  gradually  fitted  for  an  inde- 
pendent life  outside  the  protecting  body  of  the  mother. 


REPRODUCTION  19 

21.  Primary    and    secondary    sexual    characters.  - 

The  particular  characteristics  which  differentiate  the 
male  from  the  female  sex  may  be  divided  into  primary 
and  secondary  characters.  The  primary  characters  are 
those  which  are  peculiar  to  the  sex.  In  the  male,  the 
form  and  functions  of  the  generative  organs  clearly 
differentiate  him  from  the  female.  As  Lee  l  has  pointed 
out,  the  function  of  the  primary  sexual  characters  of 
the  male  is  the  production  of  spermatozoa  and  the  im- 
pregnation of  the  female  egg.  The  activities  of  the 
primary  sexual  organs  of  the  female  center  about  the 
production  of  the  egg  and  the  development  of  the 
embryo. 

The  secondary  sexual  characters  are  those  which  may 
often  be  possessed  in  common  by  both  sexes  but  experi- 
ence a  special  and  somewhat  different  development  in 
the  two  sexes.  Examples  of  secondary  sexual  characters 
are  the  horns  of  the  ram  in  some  breeds  of  sheep,  the 
spurs  of  the  cock,  the  tusks  of  the  boar,  the  various  col- 
ored plumage  of  many  male  birds,  and  the  crest  in  stal- 
lions and  bulls.  Under  certain  conditions,  the  secondary 
sexual  characters  which  are  in  general  characteristic  of 
the  male  sex  alone  may  be  developed  in  the  female.  Thus, 
hens  sometimes  develop  spurs  and  ewes  develop  horns. 

Castration  of  the  male  causes  a  check  in  the  develop- 
ment of  the  secondary  sexual  characters  and  causes  the 
male  to  approach  more  nearly  to  the  form  and  appear- 
ance of  the  female. 

22.  The  reproductive  organs  of  the  male  (Fig.  5).  — The 
organs  of  generation  in  the  male  are  :  (a)  the  testicles,  cor- 
responding to  the  ovaries  in  the  female ;  (b)  vasa  deferentia, 
or  the  ducts  leading  from  the  testicles  to  the  ejaculatory 

1  "American  Text  Book  of  Physiology,"  1903,  p.  443. 


20  THE  BREEDING  OF  ANIMALS 

duct;  (c)  vesiculse  seminales;  (d)  prostate  glands;  (e) 
Cowper's  gland ;  (/)  urethra,  through  which  the  urinary 
and  genital  secretions  are  conveyed;  (g)  the  penis, 
through  which  the  semen  of  the  male  is  conveyed  to  the 
female  genital  organs.  The  secretions  of  the  vesiculse 
seminales,  the  prostate,  and  the  Cowper's  gland  all  empty 
into  the  urethra,  where  they  mix  with  the  seminal  fluid 
from  the  testicles.  The  testicles,  vasa  deferentia  and 
urethra  and  penis  are  often  called  the  essential  organs  of 
generation,  while  the  remaining  three  are  referred  to  as 
the  accessory  organs. 

23.  The  testicles.  —  The  essential  sexual  elements, 
the  spermatozoa,  are  formed  in  the  testicles.  The  removal 
of  the  testicles,  therefore,  destroys  the  ability  of  a  male 
animal  to  elaborate  the  male  germ-cells  and  permanently 
destroys  his  fecundity.  The  structure  of  the  testis  is 
described  in  some  detail  by  Marshall  as  follows  : 1  "  This 
organ  is  enclosed  within  a  fibrous  capsule,  the  tunica 
albuginea,  which  is  very  rich  in  lymphatics.  It  is  cov- 
ered by  a  layer  of  serous  epithelium  reflected  from  the 
tunica  vaginalis.  Posteriorly  the  capsule  is  prolonged 
into  the  interior  of  the  testis  in  the  form  of  a  mass  of 
fibrous  tissue  (the  mediastinum  testis).  Certain  other 
fibrous  processes  or  trabeculse  also  project  inwards  from 
the  capsule,  and  divide  the  glandular  substance  into 
lobules.  The  efferent  ducts  of  the  testis  (vasa  efferentia) 
open  into  a  single  convoluted  tube  situated  at  the  pos- 
terior margin  of  the  organ  and  attached  to  the  medias- 
tinum. This  is  the  epididymis.  Its  lower  extremity 
is  prolonged  into  a  thick-walled  muscular  tube  (the  vas 
deferens)  which  is  the  passage  of  exit  for  the  seminal 
fluid  or  sperm-containing  secretion.  The  glandular  sub- 

1  Marshall,  "The  Physiology  of  Reproduction." 


REPRODUCTION 


21 


FIG.  5.  —  Genital  organs  of  boar.  1,  testicle;  2,  epididymis;  3, 
vas  deferens ;  4,  spermatic  artery ;  5,  vesicula  seminalis ;  6,  prostate ; 
7,  Cowper's  gland ;  8,  bulbo  cavernosus  muscle ;  9,  9'  and  9",  penis ; 
10,  retractor  penis  muscle ;  12,  orifice  of  preputial  pouch. 


22  THE  BREEDING  OF  ANIMALS 

stance  of  the  testis  is  composed  of  the  convoluted  seminif- 
erous tubules,  two  or  three  of  which  join  together  to 
form  a  straight  tubule  which  passes  into  the  body  of 
the  mediastinum.  The  straight  tubules  within  the 
mediastinum  unite  in  their  turn,  giving  rise  to  a  network 
of  vessels  called  the  rete  testis.  From  the  rete  the  vasa 
efferentia  are  given  off.  Between  the  tubules  is  a  loose 
connective  tissue  containing  a  number  of  yellow  epithelioid 
interstitial  cells.  The  connective  tissue  also  contains 
numerous  lymphatics  and  blood-vessels  (branches  of  the 
spermatic  artery).  The  nerves  of  the  testis  are  derived 
from  the  sympathetic  system,  but  a  few  filaments  come 
from  the  hypogastric  plexus." 

The  male  reproductive  organs 1  other  than  the  testicles 
are  chiefly  concerned  in  providing  for  the  transmission  of 
the  fully  mature  sperm-cells  from  the  testicles.  The 
seminal  fluid  is  secreted  by  the  seminiferous  tubules  and 
after  expulsion  is  mixed  with  other  fluids  from  the  male 
accessory  organs. 

The  function  of  the  seminal  fluid  seems  to  be  to  pro- 
vide a  favorable  medium  for  the  spermatozoa. 

24.  Castration.  —  The  removal  of  the  testicles  of  the 
male  results  in  profoundly  influencing  not  only  the  breed- 
ing function  of  the  animal  but  in  marked  bodily  change. 
While  the  testicles  seem  to  have  no  important  connec- 
tion with  or  relation  to  the  body-cells  and  their  removal 
interferes  in  no  way  with  the  normal,  healthy  function- 
ing of  the  other  bodily  organs,  it  is  nevertheless  true  that 
castration  materially  influences  the  animal  economy. 

1  The  student  is  referred  to  standard  works  on  anatomy  and 
physiology  for  a  detailed  discussion  of  the  organization  and 
functional  relations  of  the  various  male  reproductive  organs. 
See  Sisson,  "Veterinary  Anatomy." 

Chauveau,  "Veterinary  Anatomy." 


REPRODUCTION  23 

If  the  young  male  is  castrated,  the  external  appearance 
of  the  animal  undergoes  a  gradual  change.  The  whole 
aspect  becomes  less  masculine.  The  shoulders,  neck 
and  crest  develop  relatively  to  a  much  less  extent.  The 
hind  quarters  are  relatively  better  developed  in  the 
castrated  animal.  The  temperament  and  disposition 
undergo  radical  changes.  The  bull  castrated  before 
puberty  fails  to  develop  the  heavy  head  and  horns,  curly 
hair  and  protruding  eye  characteristic  of  this  animal.  In 
swine,  castration  prevents  the  development  of  the  shoulder 
plates  and  tusks.  The  horns  of  sheep  are  very  greatly 
dwarfed,  though  the  same  effect  is  not  so  marked  in  cattle. 
The  removal  of  the  testicles  also  influences  the  physiolog- 
ical constitution  of  the  animal.  It  is  well  known  that 
oxen  grow  larger  and  heavier  than  the  uncastrated  bulls. 
The  same  result  is  observed  in  capons  which  often  grow 
to  a  much  greater  weight  than  the  normal  male.  The 
castration  of  old  boars  results  in  the  disappearance  of 
the  strong  odor  characteristic  of  the  flesh,  and  their  food 
value  is  thereby  increased. 

The  removal  of  the  ovaries  (spaying)  of  the  female 
is  followed  by  phenomena  similar  to  those  observed  in 
the  castrated  male.  The  spayed  female  loses  her  feminine 
appearance  and  approaches  the  male  in  general  char- 
acter. Like  the  male,  the  disposition  becomes  quieter 
and  the  general  physiological  condition  of  the  animal 
favors  more  rapid  laying  on  of  fat. 

At  the  Massachusetts  Experiment  Station,  Goodale 1 
castrated  a  brown  Leghorn  cockerel  at  twenty-four  days 
old.  At  the  same  time  the  fresh  ovaries  of  two  brood 
sisters  were  cut  in  several  pieces  and  placed  under  the 
skin  of  the  castrated  cockerel.  The  bird  developed  in 

1  Goodale,  "Science,"  Vol.  40  (1914),  p.  549. 


24        THE  BREEDING  OF  ANIMALS   , 

every  external  character  like  a  female,  so  much  so  that 
expert  poultry  men  were  deceived. 

We  may  conclude  that  the  castration  of  animals  is 
successful  in  preventing  undesirable  animals  from  re- 
producing, improving  the  fattening  qualities  of  the  meat 
animals,  increasing  the  size  in  some  cases,  improving 
the  quality  of  the  flesh,  and  increasing  the  value  of  draft 
animals.1 

25.  The  reproductive  organs  of  the  female  (Plate  II).  — 
The  essential  organs  of  reproduction  in  the  female  are 
the  two  ovaries.     The  accessory  organs  are  the  Fallopian 
tubes,  the  uterus,  the  vagina,  the  vulva  and  the  mammary 
glands.     The  function  of  the  female  organs  of  generation 
is  the  production  of  the  female  germ-cells  or  ova  and, 
when  fertilized,  to  provide  nutrition  and  proper  support 
for  the  developing  embryo. 

26.  The  ovaries.  —  The  female  egg  has  its  origin  in 
the  ovary.     This  organ  is  composed  of  connective  tissue, 
blood-vessels,  nerves  and  lymphatics  enclosed  in  an  outer 
covering  —  the  epithelium.     A  cross-section  of  the  ovary 
of  any  mature  breeding  animal  will  exhibit  a  large  number 
of  follicles  or  sacs  scattered  through  its  vascular  substance 
(Fig.  6) .    The  latter  are  small,  varying  from  one-hundredth 
to  one-thirtieth  of  an  inch  in  size.2    These  small  sacs  are 
called  the  Graafian  follicles,  and  each  contains  an  ovum 
or  egg.     The  eggs  or  ova  in  these  follicles  exhibit  various 
stages  of  development,  some  being  almost  or  quite  mature, 
while    others    are    very    small    and    undeveloped.    The 
beginning  of  the  formation  of  a  Graafian  follicle  is  indi- 
cated by  a  slight  depression  in  the  surface  of  the  ovary 
which  gradually  extends  into  the  substance  of  the  ovarian 

iPusch,  "Allegemeine  Tierzucht,"  1911,  p.  153. 

2  Smith,  "Physiology  of  the  Domestic  Animals,"  p.  909. 


REPRODUCTION 


25 


FIG.  6.  —  Sections  through  ovary 
of  rat,  typical  of  ovarian  structure  in 
mammals. 


tissue  in  the  form  of  a  tubule.  Eventually  this  sac 
becomes  constricted  at  the  surface  of  the  ovary  until 
finally  the  external  opening  is  entirely  closed  and  the 
tubule  becomes  a  closed  follicle  within  the  tissues  of  the 
organ.  Within  the  follicle 
itself,  there  have  been 
formed,  in  the  meantime, 
single,  large  spherical  cells 
(primordial  germ-cells) 
from  which  one  or  some- 
times two  ova  are  devel- 
oped. The  part  of  the 
Graafian  follicle  not  occu- 
pied by  the  ovum  is  filled 
with  a  fluid  substance. 
The  follicle  increases  in  size  and  approaches  the  center  of 
the  ovary  until  near  maturity,  when  it  rises  to  the  surface 
and  finally  is  ruptured,  thus  liberating  the  enclosed  egg. 
The  bursting  of  a  Graafian  follicle  and  the  discharge 
of  the  egg  is  called  ovulation.  This  event  is  marked 
by  certain  phenomena  indicating  increased  sexual  activity. 
It  is  believed  that  menstruation  or  the  period  of  heat  in 
domestic  animals  is  coextensive  with  the  ripening  of 
the  egg.  It  is  true,  however,  that,  under  some  circum- 
stances, ovulation  may  occur  before  or  after  the  period 
of  heat.  The  ripening  of  the  first  Graafian  follicle  in 
general  marks  the  beginning  of  puberty,  but  has  been 
known  to  occur  even  in  infancy.  In  animals  generally 
ovulation  does  not  occur  during  pregnancy,  but  there 
are  numerous  exceptions  to  this  rule,  as  will  be  described 
later  in  the  case  of  some  animals  which  have  come  in  heat 
and  have  even  conceived  again,  although  pregnant  at 
the  time  (Fig.  7). 


26 


THE  BREEDING  OF  ANIMALS 


w. 


FIG.  7.  —  Genital  organs  of  mare.  1,  ovary ;  2,  Fallopian  tube ;  2', 
fimbriated  end  of  Fallopian  tube ;  3,  uterus ;  5,  horn  of  uterus ;  6  and 
6',  cervix ;  7,  broad  ligament  of  uterus ;  9,  vagina ;  10,  vulva ;  13  and 
13',  lips  of  vulva ;  14,  clitoris ;  15,  urinary  bladder ;  a,  utero-ovarian 
artery  with  branches  to  ovary  (a)  and  uterus  (a") ;  6,  uterine  artery. 


REPRODUCTION  27 

Some  of  the  domestic  animals  do  not  come  in  heat 
while  suckling  young,  while  others  discharge  eggs  and 
undergo  the  periodical  phenomenon  of  heat  as  readily 
during  lactation  as  at  any  other  time. 

27.  The  Fallopian  tubes.  —  The  egg  which  has  been 
discharged  as  the  result  of  the  processes  described  above 
finds  its  way  to  the  uterus  through  the  Fallopian  tubes 
in  mammals  or  the  oviduct  in  birds.  These  are  small, 
very  crooked  canals  leading  from  the  ovary  to  the  uterus. 
This  accessory  organ  is  not  rigidly  joined  to  the  ovary 
by  tissues,  but  the  end  nearest  the  ovary  is  mostly  free 
to  move  to  different  sides  of  the  ovary.  The  ovarian 
end  of  the  Fallopian  tube  is  expanded  into  a  fimbriated 
extension  which  spreads  out  not  unlike  the  fingers  of  the 
hand.  The  comparison  will  be  still  more  exact  if  we  con- 
ceive of  the  fingers  of  the  hand  as  being  connected  by 
web-like  tissues. 

In  many  mammals,  the  tube  is  lined  with  cilia  which 
move  from  the  ovary  toward  the  uterus.  In  normal 
cases  when  the  egg  is  discharged  from  the  ovary,  the 
fimbriated  expansion  of  the  Fallopian  tube  clasps  the 
ovary  at  the  point  where  the  Graafian  follicle  bursts 
through  its  walls.  The  ciliary  movement  within  the  tube, 
assisted  by  muscular  movements  of  the  tube  itself,  carries 
the  egg  from  the  ovary  to  the  uterus.  The  time  required 
for  the  passage  of  the  egg  through  the  Fallopian  tube  has 
not  been  definitely  determined  for  all  mammals,  but  is 
known  to  vary  from  three  to  eight  days. 

The  union  of  the  spermatozoon  and  the  egg  usually 
takes  place  in  the  Fallopian  tube.  To  accomplish  this 
union,  it  is  necessary  for  the  sperm-cell  to  pass  into  the 
uterus  and  up  into  the  tube.  This  it  is  able  to  do  by 
reason  of  its  possessing  the  power  of  independent  motion. 


28  THE   BREEDING   OF  ANIMALS 

28.  The  uterus.  —  The  uterus  is  a  muscular  sac  con- 
necting the  Fallopian  tubes  and  the  vagina  in  which  the 
development  of  the  fertilized  egg  is  carried  forward  until 
expelled  from  the  body  of  the  mother  at  the  time  of  par- 
turition (Figs.  8,  9,  10). 

In  many  mammals  the  uterus  divides  into  two  tubes 
called  horns.  Each  horn  is  connected  with  the  corre- 
sponding ovary  by  means  of  the  Fallopian  tube. 

The  portion  of  the  uterus  nearest  the  vagina  is  some- 
what constricted  to  form  the  cervix  or  neck  of  the  uterus. 
The  vagina  connects  the  uterus  with  the  external  genitals 
called  the  vulva. 

29.  The  mammary  glands.  —  The  possession  of  mam- 
mary glands  whose  function  is  the  elaboration  of  food 
materials   for   the   young    offspring  is   characteristic  of 
all  mammals.     These  glands  are   highly   developed  and 
functional  in  the  fertile  female,  but  are  also  present  in 
rudimentary  form  in  the  male.     In  rare  cases  the  rudi- 
mentary glands  present  in  the  male  have  been  known 
to  function.     Hay  ward    at   the    Delaware    Experiment 
Station  reports  the  case  of  a  registered  Guernsey  bull 
owned    by    that    institution    whose    mammary    glands 
were    developed    to   the   extent   of    producing    a    small 
amount  of  milk.     Milk  has  also  been  produced  from 
the  rudimentary  mammary  glands  of    male  goats  and 
sheep.     In  man  the  rudimentaries  of  males  have  pro- 
duced milk  at  birth  and  at  puberty  and  in  exceptional 
cases    at    other    times.     The    number    of    nipples   in  a 
species  bears   some   relation   to  the   normal  number  of 
young  produced   in   a  litter,  and   also   to  the  needs  of 
the  young  animal.     The  glands  are  generally  arranged 
in  pairs  either  along  the  ventral  side  of  the  thorax  or 
abdomen. 


30 


THE   BREEDING   OF  ANIMALS 


FIG.  9.  —  Genital  organs  of  the  sow.  1,  lips  of  vulva ;  2,  clitoris ; 
3,  vulva ;  4,  external  opening  of  urethra  ;  5,  vagina  ;  5,  cervix  ;  6,  body  of 
uterus ;  7,  horn  of  uterus ;  7',  horn  of  uterus  opened  to  show  interior ; 
8,  Fallopian  tube ;  8',  abdominal  opening  of  Fallopian  tube ;  9,  ovaries ; 
12,  urinary  bladder. 


REPRODUCTION  31 

30.  Structure  of  mammary  glands.1  —  The  mammary 
glands  are  made  up  of  lobes  which  in  turn  are  further 
divided  into  lobules.  The  latter  arise  from  secretory 
alveoli.  The  lobule  is  chiefly  connective  tissue  binding 
together  the  milk  ducts.  The  alveoli  unite  together 
to  form  the  lactiferous  ducts  which  open  externally. 
These  ducts  are  provided  with  reservoirs  wherein  the 
milk  is  accumulated  during  the  period  of  active  lac- 
tation. During  lactation  the  alveoli  secrete  milk.  This 
secretion  goes  forward  at  all  times,  but  is  particularly 
active  during  suckling.  The  milk  drawn  first  is  of 
poorer  composition  in  respect  to  solids  than  that  drawn 
near  the  end  of  the  milking.  This  may  be  due  to  the 
fact  that  the  larger  globules  pass  through  the  ducts 
with  greater  difficulty  and  are  thus  retained  longer  in 
the  gland. 

The  processes  concerned  in  milk  secretion  are  not 
entirely  understood,  at  least  three  views  having  been 
held.  One  hypothesis  is  that  the  secretory  cells  them- 
selves break  down  and  thus  set  free  their  contents  as  is  the 
case  with  the  sebaceous  glands.  Another  view  is  that 
the  milk  is  simply  excreted  from  the  cell  without  causing 
the  breaking  down  of  the  cell,  in  a  manner  similar  to 
that  which  occurs  in  many  secretory  glands. 

"  The  third  theory 2  was  first  suggested  by  Langer, 
and  has  since  been  adopted,  with  various  slight  modifi- 
cations, by  Heidenhain,  Steinhaus,  Brouha  and  others. 
According  to  their  view  the  cells  of  the  gland  lengthen 
out,  so  that  their  ends  come  to  project  freely  into 
the  lumina  of  the  alveoli.  The  projecting  portions 
then  undergo  a  process  of  disintegration  before  or  after 

1  Marshall,  "The  Physiology  of  Reproduction,"  p.  553. 

2  Ibid.,  p.  560. 


FIG.  10.  — Genital 
organs  of  bitch,  a, 
ovarian  bursa ;  b, 
opened  to  show  ova- 
ry ;  c,  ovary ;  d,  d, 
horns  of  uterus ;  e,  e', 
body  of  uterus ;  /, 
neck  of  uterus;  /', 
cervix  (os  uteri) ;  g, 
vagina;  i,  vulva;  k, 
opening  of  urethra ; 
I,  urinary  bladder ; 
m,  urethra ;  n,  n,  lips 
of  vulva ;  p,  clitoris. 
Vulva,  vagina  and 
uterus  cut  open  to 
show  interior. 


2" 
32 


REPRODUCTION  33 

becoming  detached,  and  the  cell  substance  passes  into 
solution  to  form  the  albuminous  and  carbohydrate  con- 
stituents of  the  milk.  The  fat  droplets  which  collect  in 
the  disintegrating  part  of  the  cell  give  rise  to  the  milk 
fat.  The  basal  portions  of  the  cell  remain  in  position 
without  being  detached,  and  subsequently  develop  fresh 
processes,  which  in  their  turn  become  disintegrated.  It 
is  believed,  however,  that  some  cells  simply  discharge 
their  fat  droplets  and  other  contents  into  the  lumina, 
while  otherwise  remaining  intact." 

31.  Fertilization  of  the  ovum.  —  We  have  seen  how 
growth  may  continue  for  a  long  period  by  successive 
cell  division.  Indeed,  in  many  of  the  simpler  forms, 
Wilson  has  pointed  out  that  "  as  far  as  we  can  see  from 
an  a  priori  point  of  view,  there  is  no  reason  why,  barring 
accident,  cell  division  should  not  follow  cell  division  in 
endless  succession  in  the  stream  of  life."  1 

In  some  of  the  very  simplest  forms,  no  sexual  union 
has  so  far  been  discovered.  But,  under  normal  conditions, 
reproduction  without  sexual  union  is  rare  and  practically 
unknown  in  the  higher  animals.  The  impetus  to  growth 
and  cell  division  is  not  permanent  and  must  be  constantly 
renewed.  The  stimulus  to  renewed  growth  is  accom- 
plished by  the  definite  mixture  of  living  protoplasm  from 
two  entirely  distinct  individuals.  This  process  of  fertili- 
zation involves  a  union  of  the  ovum  of  the  female  and 
the  spermatozoon  of  the  male.  This  union  is  the  begin- 
ning of  the  life  of  each  individual  and  results  not  only 
in  energizing  the  protoplasm  of  the  germ-cell,  causing  it 
to  divide  and  grow,  but  the  admixture  of  germ  material 
from  two  different  individuals  introduces  into  the  new 
organism  two  distinct  lines  of  inheritance.  . 

i  Wilson,  "The  Cell." 


34  THE   BREEDING   OF   ANIMALS 

32.  The  nature   of  fertilization.  —  The  essential   na- 
ture of  fertilization  still  remains  a  matter  of  discussion. 
It  may  be  that  the  fertilization  of  the  egg  is  primarily 
a  rejuvenescence  of  the  protoplasmic  material  which,  for 
some  at  present  unknown  reason,  has  lost  the  power  of 
further  growth  through   cell   division.     This   view   was 
held  by  Butschli,  Hertwig,  Minot,  Engelman  and  others. 
Even  in  the  simpler  forms  of  life  where  anything  like 
sexual  union  is  absent,  the  cycle  of  growth  is  continually 
reinaugurated  by  the  conjugation  of  independent  cells. 
In  all  higher  forms  the  egg  is  stimulated  to  growth  and 
cell  division  by  the  introduction  of  the  sperm. 

Weismann  has  looked  upon  fertilization  as  a  source 
of  variation  and  has  maintained  that  this  should  be 
regarded  as  the  chief  function  of  this  process.  Both 
the  theory  of  rejuvenescence  and  that  which  regards 
this  process  as  chiefly  a  source  of  variation  are  in  accord- 
ance with  the  observations  of  practical  breeders.  Cross- 
breeding is  known  to  induce  greater  vigor  and  increased 
fecundity  and  at  the  same  time  to  break  up  the  fixed 
characters  of  the  breed  or  type.  It  is  equally  well  estab- 
lished that  under  certain  conditions  in-breeding  tends  to 
identity  of  character  and  results  in  sterility  and  weakness 
of  constitution.  But,  after  all,  the  real  purpose  and  na- 
ture of  sexual  union  in  reproduction  is  still  an  unsolved 
problem. 

33.  The  process  of  fertilization.  —  The  ultimate  pur- 
pose of  the  sexual  union  of  animals  is  to  insure  the  fertili- 
zation of  the  egg  by  the  spermatozoon.     When  the  egg 
and  sperm  meet  within  the  generative  organs  of  the  fe- 
male, significant  and  important  changes  are  set  in  motion, 
which  eventually  result  in  an  admixture  or  union  of  the 
germ  substance  of  the  two  parents.     These  changes  are 


REPRODUCTION  35 

primarily  concerned  with  the  nuclei  of  the  egg  and  the 
sperm. 

In  most  species  of  animals,  there  is  a  definite  attrac- 
tion existing  between  the  egg  and  the  sperm-cell,  which 
causes  the  spermatozoon  to  attach  itself  to  and  finally 
penetrate  the  egg.  This  attraction  is  probably  of  a 
chemical  nature.  Pfeffer  found  that  solutions  of  malic 
acid  were  as  successful  in  attracting  the  sperm-cells  of 
ferns  as  the  substance  which  was  thrown  off  by  the  female 
sex  cells.  In  other  experiments,  other  chemical  sub- 
stances have  exhibited  a  specific  attraction  for  the  sperm. 
The  seat  of  this  chemical  substance  which  pulls  the 
sperm  to  the  egg  seems  to  be  located  in  the  cytoplasm  of 
the  egg  and  not  in  the  nucleus. 

The  point  at  which  the  spermatozoon  enters  the  egg 
is  often  predetermined  by  the  existence  of  a  depression 
or  opening  (micropyle)  in  the  wall  of  the  ovum.  In 
some  cases,  there  exists  a  special  protoplasmic  attraction 
cone  at  which  point  the  sperm  enters  the  egg.  The 
entrance  of  the  sperm  in  most  cases  is  followed  rapidly 
by  the  formation  of  a  vitelline  membrane  which  surrounds 
the  egg  and  prevents  the  entrance  of  other  spermatozoa. 

Normally  in  mammals  one  sperm  only  enters  the  egg. 
When  through  accident  two  or  more  spermatozoa  enter 
the  substance  of  the  egg,  the  developmental  changes  are 
abnormal  and  the  daughter  nucleus  soon  dies. 

34.  The  chromosomes.  —  When  the  germ  nuclei  unite 
to  form  the  daughter  nucleus  of  the  new  cell,  it  seems 
probable  now  that  the  chromatin  substance  does  not  fuse 
in  true  fashion  but  the  chromosomes  may  lie  side  by  side 
within  the  nucleus  of  the  new  cell.  It  is  not  definitely 
determined  that  these  chromosomes  remain  thus  separate 
and  apart  throughout  the  life  of  the  cell,  but  such  may  be 


36  THE  BREEDING  OF  ANIMALS 

the  case.  After  the  reduction  of  the  chromosomes  in 
the  maturation  of  the  germ-cells  and  accompanying  the 
formation  of  the  polar  bodies,  the  number  of  chromosomes 
is  reduced  to  one-half  the  number  existing  in  the  body- 
cells  and  these  uniting  with  an  equal  number  from  the 
sperm  constitute  the  normal  number  characteristic  of 
the  tissue  cells.  As  Wilson  says,  "  We  have  thus  what 
must  be  reckoned  as  more  than  a  possibility  that  every 
cell  in  the  body  of  the  child  may  receive  from  each  parent 
not  only  half  of  its  chromatin  substance,  but  one-half 
of  its  chromosomes,  as  distinct  and  individual  descendants 
of  those  parents." 

35.  Results  of  union  of  egg  and  sperm.  —  Extraor- 
dinary changes  follow  immediately  the  physical  union 
of  the  egg  and   spermatozoon.     These  changes  are  of 
the  most  fundamental   significance  in  connection  with 
discussions  of  development  and  inheritance. 

36.  Changes   in   the    ovum.  —  The   entrance   of   the 
sperm  seems  to  exert  an  influence  which  permeates  the 
entire  constitution  of  the  egg  substance.     Various  and 
important  changes  now  take  place,  ending  finally  in  an 
exact  union  of  the  germ  substance  of  the  two  sex  cells, 
thus  forming  the  new  or  daughter  cell.     The  daughter 
cell  is  the  beginning  of  a  new  individual  and  becomes  the 
offspring  of  the  parents,  from  which  the  sperm  and  ovum 
were   derived.     When   the    sperm    enters   the   egg,    the 
vitelline  membrane  is  thrown  around  the  outside  of  the 
ovum.     The  nucleus  of  the  egg,  which  is  now  called  the 
germinal  vesicle,  moves  to  the  wall,  and  changes  occur 
which  result  in  the  formation  of  the  polar  bodies.     This 
process  prepares  the  germ  nucleus  of  the  egg  for  ferti- 
lization. 

The  polar  bodies  are  formed  by  successive  divisions 


REPRODUCTION  37 

of  the  egg  nucleus.  During  their  formation,  the  number 
of  chromosomes  characteristic  of  the  species  is  reduced 
by  half,  so  that  when  the  egg  nucleus  is  finally  ready  for 
union  with  the  sperm  nucleus,  it  contains  exactly  one-half 
the  number  of  chromosomes  usually  present  in  the  cell. 
There  are  formed  in  all  three  polar  bodies.  The  divisions 
which  occur  in  their  formation  separate  the  mass  of 
chromatin  originally  present  in  the  germinal  vesicle 
into  four  equal  parts.  One-fourth  part  enters  the  egg 
nucleus  and  the  other  three  parts  are  distributed,  one  to 
each  of  the  polar  bodies.  The  polar  bodies  are  in  no 
direct  way  concerned  in  fertilization  and  soon  disinte- 
grate and  disappear. 

37.  Changes   in  the   spermatozoon.  —  After   contact 
with  the  egg,  the  tail  of  the  sperm  soon  degenerates 
either  outside  or,  in  some  cases,  inside  the  egg. 

The  nucleus  of  the  sperm  grows  rapidly  in  size.  The 
nucleus  is  further  stimulated  to  cell  division  by  the 
influence  of  the  cytoplasm  of  the  egg. 

38.  The  significance  of  reduction.  —  All   the  phenom- 
ena attending    the    processes    of    fertilization    seem  to 
have  been  specifically  arranged  for  the  purpose  of  bringing 
about  a  reduction  of  the  number  of  chromosomes  in  the 
germ-cells  to  one-half  that  found  in  the  other  cells  of  the 
body.     A  result  so  universal  in  plants  and  animals  must 
possess  some  significance  in  the  reproduction  of  living 
forms.     This  change  is  characteristic  of  the  germ-cells 
only  and  always  occurs  prior  to  and  in  preparation  for 
the  union  of  the  spermatozoon  and  the  egg.     What  is 
the  real  significance  of  the  reduction  of  the  chromosomes  ? 
Is  this  reduction  of  the  chromatin  a  quantitative  one,  or 
is  it  in  some  way  a  qualitative  division?    It  must  be 
admitted  that  we  cannot  yet  give  positive  answers  to 


38  THE   BREEDING   OF  ANIMALS 

these  questions.  That  this  process  is  one  of  fundamental 
significance  and  is  intimately  connected  with  the  problem 
of  how  characters  are  transmitted,  is  certain.  Mani- 
festly its  purpose  is  to  provide  for  a  constant  number  of 
chromosomes  in  the  body  tissues.  It  is  not,  as  some  have 
maintained,  a  mere  mass  reduction  of  the  chromatin. 
Weismann's  ingenious  theory  of  the  germ-plasm  attempts 
to  explain  the  process  and  to  point  out  the  hereditary 
significance  of  reduction.  In  an  earlier  investigation, 
Roux  held  that  the  hereditary  qualities  are  represented 
by  the  individual  chromatin  granules.  During  cell  di- 
vision, these  arranged  themselves  side  by  side  in  the 
spireme  thread,  and  the  splitting  of  the  spireme  thread 
longitudinally  actually  resulted  in  halving  each  indi- 
vidual chromatin  granule.  Quoting  Wilson,1  —  "  Roux 
assumes,  as  a  fundamental  postulate,  that  division  of  the 
granules  may  be  either  quantitative  or  qualitative.  In 
the  first  mode,  the  group  of  qualities  represented  in  the 
mother  granule  is  first  doubled  and  then  split  into  equiva- 
lent daughter  groups,  the  daughter  cells,  therefore,  receiv- 
ing the  same  qualities  and  remaining  of  the  same  nature. 
In  '  qualitative  division,'  on  the  other  hand,  the  mother 
group  of  qualities  is  split  into  dissimilar  groups,  which, 
passing  into  the  respective  daughter  nuclei,  lead  to  a 
corresponding  differentiation  in  the  daughter  cells.  By 
qualitative  divisions,  occurring  in  a  fixed  and  predeter- 
mined order,  the  idioplasm  is  thus  split  up  during  ontogeny 
into  its  constituent  qualities  which  are,  as  it  were,  sifted 
apart  and  distributed  to  the  various  nuclei  of  the  embryo. 
Every  cell  nucleus,  therefore,  receives  a  specific  form  of 
chromatin  which  determines  the  nature  of  the  cell  at  a 
given  period  in  its  later  history.  Every  cell  is  thus 

1  Loc.  cit. 


REPRODUCTION  39 

endowed  with  a  power  of  self-determination  which  lies 
in  the  specific  structure  of  its  nucleus,  and  its  course  of 
development  is  only  in  a  minor  degree  capable  of  modi- 
fication through  the  relation  of  the  cell  to  its  fellows." 

Weismann  conceives  that  the  chromatin  (idioplasm) 
of  the  germ-cell  exists  in  the  form  of  minute  particles 
which  combine  to  form  aggregates,  and  these  again  unite 
to  form  compound  groups  and  so  on  until  finally  we  have 
the  chromosomes.  He  calls  the  smallest  groups  deter- 
minants, the  next  larger  groups  ids  (chromatin  granules), 
these  in  turn  combining  and  forming  idants  or  chro- 
mosomes. Weismann  in  explanation  of  his  theory  says: 
"  Ontogeny  depends  on  a  gradual  process  of  disintegra- 
tion of  the  id  of  germ-plasm,  which  splits  into  smaller 
and  smaller  groups  of  determinants  in  the  development 
of  each  individual.  Finally  .  .  .  only  one  kind  of 
determinant  remains  in  each  cell,  viz.  that  which  has  to 
control  that  particular  cell  or  group  of  cells.  In  this 
cell  it  breaks  up  into  its  constituent  biophores  and  gives 
the  cell  its  inherited  specific  character." 

In  developing  this  theory  it  is  necessary  to  assume  a 
very  stable  condition  of  the  germ-plasm.  For  example, 
one  must  assume  that  some  portion  of  the  original  germ- 
plasm  is  passed  on  to  the  germ  nucleus  unchanged  in 
structure  from  generation  to  generation. 

The  theories  of  both  Roux  and  Weismann  are  in  part 
only  based  upon  demonstrated  phenomena  occurring  in 
the  cell.  Some  of  the  most  fundamental  and  far-reaching 
postulates  of  these  theories  are  highly  speculative  and 
cannot  be  demonstrated  by  any  known  method  of  re- 
search. It  must  be  admitted,  however,  that  Weismann's 
theory  of  the  germ-plasm  with  some  modifications  comes 
nearer  to  an  adequate  explanation  of  the  changes  which 


40  THE   BREEDING   OF  ANIMALS 

can  actually  be  observed  in  the  cell  during  the  fertiliza- 
tion and  maturation  of  the  germ-cells  than  any  other  so 
far  advanced. 

39.  The  origin  of  the  germ-cells.  —  The  origin  of  the 
germ-cells  and  the  phenomena  attending  the  process  of 
the  reduction  of  the  chromosomes  are  of  great  fundamental 
significance.     The  functions  of  the  chromatin  in  modern 
theories  of  heredity,  the  particular  meaning  of  the  pro- 
cesses which  result  in  reducing  the  number  of  chromosomes 
to  one-half  that  found  in  the  body-cells,  are  problems 
of  the  greatest  interest  in  modern  biology. 

The  maturation  of  the  germ-cells  is  brought  about 
by  similar  processes  in  the  egg  and  sperm.  The  impor- 
tant result  which  is  the  reduction  of  the  number  of  chro- 
mosomes is  accomplished  in  each.  This  is  brought  about 
finally  in  the  last  two  maturation  divisions  resulting  in  four 
cells,  each  of  which  contains  but  one-half  the  number  of 
chromosomes  characteristic  of  the  same  cells.  In  the 
female  three  of  the  four  cells  are  the  polar  bodies  which 
are  abortive  and  disappear.  The  remaining  cell  is  the 
ovum  and  becomes  the  carrier  of  the  hereditary  substance 
of  the  female.  In  the  male  the  reduction  divisions  occur 
as  in  the  female,  but  all  four  cells  are  functional  and  may 
take  part  in  the  process  of  fertilization. 

40.  Maturation  and  reduction  in  the  female  (oogenesis) . 
—  The  female  germ-cells  are  derived  from  the  primordial 
germ-cells  of  the  mother.     Successive  divisions  of  the 
primordial   germ-cells   result   in  the  development   of  a 
number  of  cells  known  as  oogonia. 

From  these  the  ovarian  eggs  are  directly  derived. 
Their  growth  is  characterized  by  an  increase  in  the  size 
of  the  nucleus  which  in  the  ovarian  egg  (oocyte)  becomes 
the  germinal  vesicle.  Food  materials  develop  in  the 


REPRODUCTION  41 

cytoplasm,  which  is  now  called  the  yolk.  During  all  the 
changes  described  above,  the  number  of  chromosomes 
in  the  ova  remains  the  same  as  in  the  body-cells.  When 
the  egg  undergoes  the  final  preparation  for  fertilization, 
as  we  have  seen,  the  number  of  chromosomes  is  reduced 
by  one-half. 

41.  Reduction  in  the  male  (spermatogenesis).  —  The 
changes  which  bring  about  the  reduction  of  the  chromatin 
in  the  male  germ-cell  are  almost  exactly  similar  to  those 
which  have  been  described  in  the  development  of  the 
ovarian  egg.     The  spermatozoa  originate  in  the  primor- 
dial  germ-cells.     In   their   earlier   development   by   cell 
division,  numerous  spermatogonia  are  formed  which  for 
a  time  continue  to  divide  with  the  typical  number  of 
chromosomes    found    in    the    soma-cells.     In    time    the 
spermatogonia  cease  to  divide  further  and  become  larger. 
At  this  stage  they  are  physiologically  equivalent  in  func- 
tion to  the  oocyte  of  the  female  and  are  known  as  sperma- 
tocytes.    There  now  occur  two  divisions  resulting  in  four 
cells,  each  having  but  one-half  the  typical  number  of 
chromosomes.     Unlike  the  reducing  process  in  the  female 
which  results  in  only  one  perfect  ovum  and  three  abortive 
cells,  all  four  sperm-cells  are  functionally  perfect. 

42.  The  period  of  the  oestrum  or  heat.  —  In  all  the 
domestic  mammals,  the  ripening  of  the  first  egg  is  asso- 
ciated with  the  first  appearance  of  heat.     It  is'the  first 
evidence  of  puberty  and  is  accompanied  by  the  rapid 
development  of  all  the  secondary  sexual  characters  dis- 
tinctive of  sex.     It  is  by  no  means  certain  that  the  stimu- 
lus which  causes  the  heat  or  oestrum  in  animals  originates 
in  the  ovary.     It  is  possible  that  the  stimulus  to  egg  forma- 
tion is  to  be  found  in  the  influences  set  in  motion  by  the 
oestrum  itself.     The  production  of  ova  and   the  heat 


42        THE  BREEDING  OF  ANIMALS 

period  are  so  closely  associated  that  the  stimulus,  what- 
ever it  may  be  that  causes  the  one,  will  probably  under 
normal  conditions  directly  or  indirectly  cause  the  other. 

Heape  has  maintained  that  since  it  is  known  that, 
in  various  animals,  either  menstruation  or  oestrus  may 
take  place  without  ovulation,  and  that  ovulation  may 
occur  without  the  coincidence  of  menstruation  (Leopold 
and  Mironoff,  1894)  or  of  oestrus  (fat),  the  possibility  of 
isolating  these  functions  is  demonstrated.  Thus  it  is 
no  longer  impossible  to  suppose  that,  while  they  are 
both  due  to  similar  stimulating  influences,  one  of  them 
may  be  developed  in  excess  of  the  other.1 

It  is  probable  that  heat  may  sometimes  occur  with- 
out the  production  of  an  egg,  and  it  is  possible  that  the 
production  of  an  egg  may  not  always  be  accompanied  by 
heat,  but  when  such  a  condition  exists,  it  is  to  be  regarded 
as  the  exception  and  not  the  rule.  It  is  very  clear  that 
the  oestrum  and  ovulation  are  influenced  by  nutrition. 
An  insufficient  supply  of  food,  deficient  in  the  essential 
elements  required  for  the  normal  development  of  animals, 
retards  the  first  appearance  of  heat  in  young  animals  and 
causes  irregular  periods  in  mature  animals.  Breeders 
of  live-stock  have  long  known  that  the  oestrum  can 
be  materially  influenced  by  the  method  of  feeding. 
Skillful  stockmen  feed  the  females  in  such  a  manner 
as  to  cause  them  to  be  "  gaining  "  at  mating  time.  This 
is  accomplished  by  richer  feeding  or  turning  to  fresh 
grass. 

43.  Artificial  insemination.  —  The  transfer  of  the 
semen  of  the  male  to  the  uterus  of  the  female  by  the  aid 
of  instruments  or  capsules  is  known  as  artificial  insemina- 
tion or,  more  commonly  among  practical  breeders,  as 

1  Heape,  loc.  cit.,  p.  34. 


REPRODUCTION  43 

artificial  impregnation.  The  artificial  insemination  of 
the  domestic  animals,  particularly  cows  and  mares,  has 
been  practiced  in  various  parts  of  the  world  for  many 
years.  As  early  as  the  time  of  Spallanzani 1  (1784)  arti- 
ficial insemination  was  successfully  accomplished  in 
dogs.  It  seems  probable  also  that  the  Arabs  have  been 
familiar  with  the  possibilities  of  this  practice  for  centuries.2 
The  insemination  of  mares,  cows  and  bitches  as  a  remedy 
for  sterility  has  been  demonstrated  by  Huish.3  The  Rus- 
sian investigator  Iwanoff4  was  successful  in  inducing 
pregnancy  in  rabbits  and  guinea  pigs  by  artificial  means. 
Artificial  insemination  is  employed  for  the  purpose  of 
overcoming  certain  forms  of  sterility  in  mammals,  specifi- 
cally, constriction  of  the  muscles  surrounding  the  neck 
of  the  uterus.  It  is  also  successful  in  cases  of  acid  secre- 
tions of  the  vagina  which  are  unfavorable  to  the  proper 
functioning  of  the  sperm-cells  after  they  have  been  de- 
posited in  the  generative  organs  of  the  female.  Artificial 
insemination  is  also  a  practical  method  of  extending  the 
usefulness  of  a  valuable  male,  as  by  this  means  one  male 
may  be  used  successfully  for  breeding  a  much  larger 
number  of  females. 

44.  Methods  of  artificial  insemination.  —  The  most 
common  methods  in  use  are  insemination  with  a  specially 
made  syringe  or  the  introduction  of  the  semen  in  capsules. 
By  one  method  the  semen  is  collected  from  the  vagina 
of  the  mare  after  the  service  of  the  stallion  by  introducing 
the  syringe  into  the  vagina  until  the  mouth  of  the  syringe 

Spallanzani,  "Dissertations,"  vol.  II,  1784. 
2Gautier,  "Le  Fecondation  Artificielle,"  Paris,  1889. 

3  Huish,   "The  Cause  and   Remedy  of  Sterility  in  Mares, 
Cows  and  Bitches,"  London,  4th  edition,  1899. 

4  Iwanoff,   "De  la  Fecondation  Artificielle  chez  les  Mammi- 
feres,"  Arch,  des  Sciences  Biologiques,  vol.  XII,  1907. 


44  THE  BREEDING   OF   ANIMALS 

is  immediately  over  the  cup-shaped  depression  just  in 
front  of  the  cervix.  The  semen  is  then  drawn  into  the 
syringe  and  the  instrument  introduced  into  the  vagina 
of  the  mare  to  be  artificially  bred  and  pushed  carefully 
through  the  neck  of  the  womb  to  insure  the  depositing 
of  the  semen  inside  the  uterus.  Care  should  be  taken 
not  to  introduce  the  point  of  the  syringe  into  the  opening 
to  the  bladder  which  is  only  five  or  six  inches  from  the 
external  opening  of  the  vagina.  The  transfer  of  the 
semen  to  the  waiting  mare  should  be  made  without  un- 
necessary delay  and  all  instruments  should  be  kept  at 
body  temperature  during  the  operation.  All  instruments 
should  be  thoroughly  sterilized  in  hot  water  before  using. 

Many  interesting  questions  of  biological  and  practical 
interest  are  raised  by  the  practice  of  artificial  insemina- 
tion. How  long  after  the  semen  is  collected  will  it  con- 
tinue to  be  potent?  What  external  conditions  such  as 
cold,  heat,  light  and  air  affect  the  vitality  of  the  germ? 
How  long  does  the  semen  retain  its  vitality  within  the 
reproductive  organs  of  the  female?  Partial  answers 
to  these  questions  have  been  given  through  the  investi- 
gations of  Lewis.1 

45.  Conditions  influencing  the  vitality  of  the  sperm- 
cells.  —  The  vitality  of  semen  collected  and  preserved 
at  different  temperatures  under  laboratory  conditions 
showed  great  variations.  High  temperatures  were  gen- 
erally unfavorable.  At  the  end  of  one  hour  the  percentage 
of  semen  which  was  alive  and  active  was :  at  33°  C.,  40 
per  cent ;  at  30°  C.,  45  per  cent ;  at  26°  C.,  85  per  cent,  and 
at  18°  C.,  90  per  cent.  At  the  end  of  two-and-one-half 
hours  all  the  sperm-cells  maintained  at  the  temperatures 
of  33°  C.  and  39°  C.  were  dead,  while  65  per  cent  of  the 

1  Lewis,  Oklahoma  Experiment  Station,  Bulletins  93  and  96. 


REPRODUCTION  45 

cells  were  alive  at  the  temperature  of  18°  C.,  and  45  per  cent 
of  the  cells  kept  at  a  constant  temperature  of  26°  were 
still  active.  The  sperm-cells  from  boars  of  several  breeds 
showed  similar  behavior  and  in  every  case  the  higher 
temperatures  were  unfavorable.  Semen  kept  at  a  tem- 
perature of  31  to  32°  C.  and  exposed  to  the  diffused  light 
of  the  laboratory  resulted  in  the  death  of  practically  all 
the  sperm-cells  at  the  end  of  seven  hours.  A  portion  of 
the  same  semen  protected  from  the  light  by  wrapping 
in  black  paper  showed  40  per  cent  of  the  germ-cells  alive 
at  the  end  of  the  same  time.  The  spermatozoa  exposed 
to  direct  sunlight  for  ninety  minutes  were  all  killed,  while 
the  portion  protected  from  direct  rays  of  the  sun  showed 
80  to  90  per  cent  alive  at  the  end  of  the  same  time. 

46.  Effect  of  too  frequent  breeding  on  the  sperm-cells. 
—  Lewis  1  found  that  the  number  of  sperm-cells  in  the 
semen  collected  from  the  first  service  of  a  vigorous  stal- 
lion was  428,000  to  a  cubic  millimeter.  The  stallion 
was  permitted  one  service  daily  for  nine  days.  The 
number  of  sperm-cells  diminished  rapidly  until  there 
were  only  74,300  sperm-cells  to  a  cubic  millimeter  at 
the  ninth  service.  The  continuous  and  frequent  service 
of  the  stallion  also  resulted  in  weakening  the  vitality  of 
the  sperm-cells.  The  semen  from  the  first  service  kept 
at  constant  temperature  of  13  to  21°  C.  showed  twenty- 
five  per  cent  of  the  sperm-cells  alive  after  six-and-one-half 
hours.  The  sperm-cells  in  semen  collected  from  the 
ninth  service  showed  only  five  per  cent  of  the  cells  alive 
after  six  hours.  Simple  exposure  to  the  air  seemed  to 
have  no  deleterious  effect  on  the  vitality  of  the  sperma- 
tozoa. 

The  standard  of  judging  of  the  vitality  of  the  sperm- 

1  Loc.  cit.,  p.  35. 


46  THE   BREEDING  OF  ANIMALS 

cells  in  this  investigation  was  microscopic  evidence  of 
normal  motion  and  as  pointed  out  by  Lewis  this  method 
does  not  necessarily  measure  the  ability  of  the  sperm 
successfully  to  fertilize  the  ovum.  The  addition  of  water 
to  semen  seems  to  lower  the  vitality  of  the  sperm-cells. 
The  presence  of  urine  also  has  a  retarding  influence  on 
the  activity  of  the  spermatozoa.  Sperm-cells  kept  in 
contact  with  rubber  lose  their  vitality  more  quickly  than 
when  preserved  in  a  glass  retainer. 

47.  Vitality  of  spermatozoa  within  the  female  genera- 
tive organs.  —  How  long  do  the  sperm-cells  retain  their 
vitality  after  being  deposited  in  the  generative  organs 
of  the  female  ?  The  answer  to  this  question  is  of  practical 
importance,  as  it  has  an  important  bearing  upon  the 
particular  time  or  stage  during  the  heat  at  which  the 
union  of  the  male  and  female  will  be  most  likely  to  result 
in  offspring. 

The  period  during  which  perfectly  healthy  sperm-cells 
retain  their  vitality  and  power  of  motion  under  labora- 
tory conditions  is  comparatively  short.  And  while 
the  conditions  for  a  longer  period  of  vitality  are  pre- 
sumably much  more  favorable  inside  the  generative 
system  of  the  female,  yet  investigations  on  mares  and 
sows  1  seem  to  point  to  the  fact  that  the  life  of  the  sperm- 
cells  in  the  uterus  of  the  female  is  comparatively  brief. 
This  is  contrary  to  the  opinion  of  many  practical  breed- 
ers. It  is  generally  believed  that  the  spermatozoa  retain 
their  vitality  in  the  reproductive  organs  of  the  female 
for  a  number  of  days.  It  is  stated  by  some  veterinary 
authorities  2  that  the  spermatozoa  will  live  in  the  vagina 
or  womb  of  the  mare  from  six  to  twelve  days  under  the 

1  Lewis,  Oklahoma  Experiment  Station,  Bulletin  96. 

2  Breeder's  Gazette,  vol.  43,  1903,  p.  683. 


REPRODUCTION  47 

most  favorable  conditions.  A  normal  alkaline  solution 
in  the  uterus  is  the  most  favorable  medium  for  the  long 
continued  vitality  of  the  sperm-cells.  It  is  very  often 
the  case  that  the  secretions  in  the  reproductive  organs 
of  the  mare  are  acid  and  such  a  chemical  condition  is  very 
unfavorable  to  the  continuance  of  the  life  of  the  sperm. 
It  is  true  that  the  sperm-cells  will  live  but  a  few  hours 
in  such  an  acid  medium  as  is  sometimes  found  in  the 
uterus.  A  study  of  the  literature  on  the  longevity  of 
the  sperm-cells  in  the  female  reproductive  organs  is 
somewhat  confusing.  It  is  probable  that  very  consider- 
able differences  exist  in  the  vitality  of  the  spermatozoa 
from  different  individuals,  but  even  this  is  scarcely  suffi- 
cient to  explain  the  wide  discrepancies  reported  by  vari- 
ous investigators.  Various  authors  1  have  reported  the 
presence  of  live  and  motile  spermatozoa  in  the  uterus  of 
dogs  eight  days  after  coition.  Marshall  and  Jolly  2  found 
live  sperm-cells  in  the  vasa  deferentia  of  the  rabbit  ten 
days  after  the  removal  of  the  testes,  but  all  were  dead  at 
thirteen  days.  The  sperm-cells  of  bats  are  reported  by 
Benecke  and  others  to  be  deposited  in  the  female  organs 
in  the  autumn,  there  to  remain  dormant  until  the  follow- 
ing spring.  Ovulation  is  induced  by  the  warm  weather 
of  early  spring  and  the  spermatozoa  which  have  lain 
dormant  throughout  the  hibernating  period  become  active 
and  insemination  occurs.  In  the  domestic  hen,  accord- 
ing to  Lillie,3  "  The  period  of  life  of  the  spermatozoa 
within  the  oviduct  is  considerable  as  proved  by  the  fact 
that  hens  may  continue  to  lay  fertile  eggs  for  a  period  of 

1  Hertwig,  "Handbuch  der  Entwicklungslehre." 

2  Marshall  and  Jolly,  "  The  (Estrus  Cycle  in  the  Dog."     Phil. 
Transactions.     B.,  vol.  198,  1905. 

3  Lillie,  "The  Development  of  the  Chick,"  1908,  p.  35. 


48        THE  BREEDING  OF  ANIMALS 

at  least  three  weeks  after  isolation  from  the  cock.  After 
the  end  of  the  third  week  the  vitality  of  the  spermatozoa  is 
apparently  reduced,  as  eggs  laid  during  the  fourth  and  fifth 
weeks  may  exhibit  at  the  most  abnormal  cleavage,  which 
soon  ceases.  Eggs  laid  forty  days  after  isolation  are  cer- 
tainly unfertilized  and  do  not  develop."1  That  the  sperma- 
tozoa may  continue  to  fertilize  eggs  in  the  hen  for  at  least 
twenty  days  after  coition  is  noted  also  by  Spallanzani. 

The  researches  of  Lewis  2  including  records  of  twenty- 
five  sows  showed  that  in  three  cases  only  were  the  sperm- 
cells  alive  and  active  after  twenty  hours  existence  in  the 
female  organs  of  generation.  In  two  cases  live  sperma- 
tozoa were  collected  from  the  uterus  at  the  end  of  forty 
hours.  In  most  cases  the  sperm-cells  taken  from  the 
female  organs  were  all  dead  at  the  end  of  sixteen  hours 
after  the  sow  had  been  bred  to  a  healthy  normal  boar. 
The  rupture  of  the  Graafian  follicles  was  found  to  occur 
almost  universally  during  the  last  part  of  the  heat.  "  In 
no  case  were  the  follicles  found  ruptured  during  the  first 
twenty-four  hours  of  heat  and  in  most  of  the  cases  a 
period  of  thirty  hours  elapsed  after  the  first  signs  of  heat 
before  many  of  the  egg-cells  escaped  from  the  ovary." 
In  no  case  were  the  Graafian  follicles  found  ruptured  in 
sows  which  were  examined  early  in  the  heat.  In  one  sow 
ovulation  did  not  occur  until  forty-five  hours  and  in 
another  case  seventy  hours  after  the  beginning  of  heat. 
From  the  fact  that  in  swine  the  duration  of  the  vitality 
of  the  sperm-cells  in  the  generative  organs  is  so  short  and 
that  ovulation  occurs  during  the  last  part  of  the  heat,  it 
is  apparent  that  sows  should  be  bred  during  the  last 
part  of  the  heat.  To  be  more  explicit,  the  sow  should 

1  Spallanzani,  "Dissertations,"  vol.  II,  1784. 

2  Loc.  cit.,  p.  7  et  seq. 


REPRODUCTION  49 

be  bred  not  less  than  thirty  hours  after  the  beginning 
of  heat.  In  practice,  the  animal-breeder  may  safely 
assume  that  the  normal  active  existence  of  the  sperm- 
cells  in  the  uterus  of  mammalian  animals  is'  short  and 
that  therefore  to  insure  successful  conception,  the  actual 
service  of  the  male  should  occur  very  near  to  the  time 
when  the  heat  is  at  its  height. 

48.  Effect  of  intoxication  of  the  male  parent  on  his 
offspring.  —  The  fertilized  egg  may  be  so  influenced  by 
various  environmental  factors  that  the  embryos  arising 
from  such  eggs  are  affected  in  a  definite  way.  Similar 
effects  from  factors  calculated  to  influence  the  sperm- 
cells  are  much  more  obscure.  It  is  very  difficult  from 
the  very  nature  of  the  factors  involved  to  influence  the 
sperm-cell  in  such  a  definite  way  that  the  influence  will 
directly  modify  the  offspring.  -Observations  on  this 
point  have  been  numerous  but  few  experiments  under 
proper  control  have  been  made.  In  all  experiments 
conducted  for  the  purpose  of  influencing  the  male  germ- 
cells,  it  is  necessary  to  work  through  the  animal  body. 
Under  these  circumstances  it  is  not  always  easy  to  deter- 
mine with  certainty  whether  the  modifications  resulting 
from  various  treatments  are  the  direct  result  of  the  treat- 
ment on  the  sperm-cell  or  the  secondary  effects  from  the 
changes  in  the  parental  body  itself.  Among  humans 
it  is  generally  recognized  that  indulgence  in. alcoholic 
drinks  by  the  male  results  in  various  defects  in  the  off- 
spring. In  one  observation  Lippich  studied  ninety-seven 
children  conceived  during  intoxication.  Of  this  number 
all  were  defective  except  fourteen.1  Among  seven  births 

^tockard,  "Effect  of  Intoxicating  the  Male  Parent,"  Amer- 
ican Naturalist,  vol.  47,  p.  641 ;  also  Journal  of  Heredity,  vol. 
5,  Feb.  1914. 


50  THE   BREEDING  OF  ANIMALS 

from  conceptions  during  drunkenness,  Sullivan  reports 
six  as  having  died  of  convulsions  and  the  seventh  was  still- 
born. Chronic  alcoholism  has  been  found  to  change  the 
structure  of  the  testicular  glands.  The  children  of  lead 
workers  are  known  to  be  sometimes  defective. 

Stockard  1  has  made  some  very  interesting  experiments 
which  clearly  show  that  the  sperm  may  be  so  affected 
that  the  resulting  offspring  will  be  defective.  As  a  result 
of  mating  normal  female  guinea  pigs  with  males  which 
were  in  a  state  of  intoxication  from  inhaling  alcohol  fumes, 
many  of  the  offspring  were  defective.  "  Out  of  69  full 
term  young,  of  which  54  were  born  alive,  only -33  have 
survived  and  many  of  these  are  small  and  excitable 
animals,  and  although  not  treated  themselves  have  since 
given  rise  to  defective  offspring  in  several  cases  where 
they  have  been  mated  with  another." 

If  these  results  are  confirmed,  we  must  conclude  that 
it  is  possible  to  modify  the  offspring  by  special  treatment 
of  the  paternal  parent.  Some  evidence  is  submitted 
by  this  investigation  to  show  that  the  bad  effects  are  not 
limited  to  the  immediate  offspring  but  are  transmitted 
to  subsequent  generations. 

49.  Effect  of  lead  poisoning  on  the  male  germ-cells 
as  indicated  by  the  offspring.  —  That  the  children  of 
fathers  who  work  in  lead-manufacturing  industries  are 
often  defective  has  been  observed  for  a  long  time.  Cole  2 
and  Bachhuber  have  reported  results  of  feeding  lead 
acetate  to  rabbits  and  fowls.  The  treatments  were 
given  to  male  parents  alone  and  these  were  mated  with 
normal  females.  Injury  to  the  offspring  from  such  treat- 

1  Loc.  cit. 

2  Cole    and    Bachhuber,    "Proceedings    of    the    Society   for 
Experimental  Biology  and  Medicine,"  1914,  XII,  pp.  24-29. 


REPRODUCTION  51 

ments  was  frequent.  The  offspring  of  male  rabbits 
treated  with  lead  acetate  were  smaller  and  had  distinctly 
lower  vitality  than  the  offspring  of  normal  parents  under 
similar  conditions.  The  results  from  lead-poisoning  of 
male  fowls  indicated  that  their  offspring  is  of  distinctly 
lower  vitality  than  of  offspring  from  normally  healthy 
fowls. 

The  importance  of  these  investigations  to  the  practi- 
cal breeder  lies  not  in  the  fact  that  alcohol  and  other 
poisons  may  modify  the  male  germ-cell  and  subsequently 
the  offspring,  but  that  the  sperm-cell  is  capable  of  such 
reactions  to  environmental  conditions  that  the  progeny 
are  profoundly  changed  or  their  development  entirely 
prevented.  If  the  offspring  may  be  so  modified  through 
the  sperm-cell  by  alcohol  and  lead  acetate,  then  it  is  in  all 
probability  susceptible  to  other  influences.  It  is  a  well- 
known  fact  that  many  conditions  in  ordinary  breeding 
practice  do  modify  the  birth  rate  and  the  characters  of 
the  offspring.  Certain  feeds  are  known  to  have  a  more 
or  less  definite  relation  to  the  breeding  powers.  Investi- 
gations under  proper  control  planned  to  test  the  influence 
of  special  feeds  on  the  sperm-cell  are  lacking.  At  vari- 
ous times  breeders  have  reported  that  alfalfa,  clover,  sugar 
and  other  materials  when  fed  to  breeding  females  have 
resulted  in  difficult  conception  or  in  weak  offspring. 
Whether  these  feeding  stuffs  have  an  injurious  effect  on 
the  male  germ-cell  is  not  known  and  cannot  easily  be 
determined  in  ordinary  farm  practice. 


CHAPTER  III 
THE  BREEDING  SEASON 

THE  arrival  of  puberty  or  the  breeding  age  in  the 
domestic  animals  does  not  mean  that  the  breeding  func- 
tion is  exercised  continuously  thereafter.  In  the  case 
of  all  animals,  domestic  and  wild,  there  exists  a  certain 
periodicity  in  the  process  of  reproduction.  The  phys- 
iological activities  which  result  in  the  propagation  of 
young  recur  with  a  certain  rhythm,  and  under  normal 
conditions,  there  is  a  definite  period  between  the 
birth  of  young  and  the  reappearance  of  reproductive 
activities. 

This  rhythm  may  be  disturbed  by  certain  external 
conditions,  although  in  the  higher  animals  it  recurs  with 
considerable  regularity.  The  reproductive  functions  are 
one  of  the  first  to  be  affected  by  a  marked  change  in  the 
environment.  Breeders  have  long  recognized  this  fact. 
It  has  been  observed  that  a  stallion  or  bull  imported 
from  Europe  to  America  often  fails  to  breed  well  the 
first  year.  The  same  condition  has  been  found  to  exist 
in  the  case  of  mares  and  cows. 

50.  Changed  conditions.  —  Darwin  has  described  how 
changes  in  the  ordinary  habits  of  animals  may  profoundly 
influence  their  reproductive  functions.  Animals  in  cap- 
tivity rarely  breed.  Elephants,  tigers,  lions  and  many 
other  species  when  confined  fail  to  breed  at  all  or  breed 

52 


THE  BREEDING  SEASON  53 

with  great  irregularity.  Failure  to  breed  under  these 
conditions  is  not  the  result  of  a  diseased  condition  of  the 
generative  organs ;  as  Marshall  has  said,  "  It  would  seem 
probable  that  failure  to  breed  among  animals  in  a  strange 
environment  is  due  not,  as  has  been  suggested,  to  any 
toxic  influence  on  the  organs  of  generation,  but  to  the 
same  causes  as  those  which  restrict  breeding  in  a  state 
of  nature  to  certain  particular  seasons,  in  that  the  sexual 
instinct  can  only  be  called  into  play  in  response  to  definite 
stimuli,  the  existence  of  which  depends  to  a  large  extent 
upon  appropriate  seasonal  and  climatic  changes."  1 

Among  the  domestic  animals,  the  generative  functions 
are  more  active  in  the  spring  season.  This  is  true  of 
the  horse,  the  cow  and  the  pig.  Sheep  breed  more  readily 
in  the  autumn. 

How  much  the  increased  sexual  activity  of  the  domestic 
animals  may  be  due  to  climate  and  how  much  to  the 
change  in  the  food  supply,  it  is  not  easy  to  determine. 
Food  itself  as  distinct  from  climate  has  a  direct  influence 
on  the  breeding  powers  of  animals.  The  green  succulent 
grass  upon  which  the  animals  feed  in  the  spring  may  be 
the  efficient  cause  of  increased  sexual  activity  at  that 
season.  The  ewes  that  exhibit  an  increased  tendency  to 
reproduction  in  the  autumn  may  be  stimulated  in  a  similar 
manner  by  the  general  abundance  of  fresh  feed  which  is 
characteristic  of  that  season.  It  has  long  been  the  cus- 
tom among  skillful  shepherds  to  provide  fresh,  succulent 
feed  in  abundance  to  ewes  at  the  time  of  turning  in  the 
rams.  This  practice  is  called  "  flushing."  The  shepherds 
claim  that  this  practice  causes  the  ewes  to  come  in  heat 
more  promptly  and  with  greater  regularity.  It  is  also 
claimed  that  a  larger  number  of  lambs  will  be  produced 

1  Marshall,  "The  Physiology  of  Reproduction,"  p.  5. 


54  THE   BREEDING   OF   ANIMALS 

at  lambing  time  as  a  result  of  this  practice.  It  is  undoubt- 
edly true  that  the  practice  stimulates  sexual  activity 
and  does  cause  the  ewes  to  come  in  heat  with  greater 
regularity.  It  is  probable  that  this  result  is  due  both 
to  the  character  of  the  feed  and  its  abundance. 

The  breeding  season  may  be  influenced  by  heredity. 
Certain  breeds  of  sheep  will  breed  readily  at  all  seasons. 
The  Dorset  Horned  breed  comes  in  heat  and  breeds  at 
all  seasons,  while  most  of  the  mutton  and  merino  sheep 
breed  readily  only  in  the  fall.  Other  conditions  which 
are  known  to  influence  the  breeding  season  in  domestic 
animals  are  the  kind  of  food,  condition  of  the  animal, 
age  and  breed. 

Evvard  *  has  shown  that  sows  gaining  in  weight  when 
bred  produced  larger  litters  than  sows  that  were  fed  only 
a  maintenance  ration. 

51.  Phases  of  the  breeding  season.  —  The  breeding 
season  is  divided  into  more  or  less  distinct  phases  and 
these  have  been  described  and  named  by  Heape  2  and 
Marshall  as  the    procestrum,  oestrum,  metoestrum  and 
dioestrum. 

52.  Prooestrum.  —  The  first  part  of  the  sexual  season 
is  occupied  by  the  procestrum.     This  period  is  character- 
ized by  marked  changes  in  the  generative  organs,  the 
uterus    becoming    congested,   while  in  the  later  stages 
there  is  often  a  flow  of  blood  from  the  external  opening 
of  the  vagina.     The  procestrum  is  the  period  often  re- 
ferred to  by  breeders  as  the  time  when  an  animal  is  "  com- 
ing in  heat  "  or  coming  in  season.3 

1  Evvard,  in  "Report  of  American  Breeders'  Association," 
191. 

2  Heape,  Quarterly  Journal  of  Microscopical  Science,  vol.  44, 
p.  1. 

3  Marshall,  "The  Physiology  of  Reproduction,"  p.  36. 


THE   BREEDING  SEASON  55 

53.  (Estrum.  —  The   oestrum    may  be  referred  to  as 
the  heat  proper  and  represents  the  time  when  the  female 
will  receive  the  male.     It  is  during  this  period  that  the 
peculiar  symptoms  well  known  to  practical  breeders  are 
exhibited.     This    phase    is    characterized    by    unusual 
activity  on  the  part  of  the  animal.     Great  restlessness, 
constant  movement  and  often  great  mental  excitement 
are  observed  in  animals  which  are  in  heat.     The  genital 
organs    become    congested.     The    mammary    glands    in 
animals  not  suckling  young  increase  in  size.     The  external 
genitals,  particularly  the  vulva,  become  swollen  and  red 
and  mucous  and  bloody  excretions  flow  from  the  genera- 
tive organs.     In  many  animals,  there  are  frequent  at- 
tempts at  urination.     The  female  sometimes  utters  loud 
cries  or  grunts,  as  in  the  sow.     Cows,  ewes  and  sows 
lose  appetite,  and  get  "  off  feed,"  often  losing  in  weight. 
In  all  meat-producing  animals,  when  the  females  are 
fattened  for  the  markets,  this  is  an  economic  loss  to  the 
feeder.     In  some  sections,  the  larger  feeders  have  spayed 
the  heifers  intended  for  fattening  and  thus  prevented 
this  loss.     If  the  animal  is  bred  and  conception  occurs, 
these  periods  of  excitement  are  prevented,  but  pregnant 
fat  animals  are  less  valuable  on  the  market  and  are  always 
discriminated  against  by  the  buyer. 

54.  Metcestrum.  —  The    oestrum    is    followed    by    a 
gradual  subsidence  of  the  symptoms  which  characterize 
this  period,  provided  coition  does  not  take  place  and 
pregnancy  result.     In  the  latter  case,  oestrum  is  followed 
by  gestation.     If  the  female  is  not  bred  to  the  male  during 
oestrum,  the  sexual  excitement  of  the  period  gradually 
passes  away  and  the  animal  returns  to  a  normal  condition. 

55.  Diosstrum.  —  The  dioestrum  represents  the  time 
of  rest  for  the  generative  system  between  the  periods  of 


56  THE  BREEDING  OF   ANIMALS 

sexual  activity.  This  varies  greatly  in  different  animals. 
Again  quoting  Marshall,  "  In  some  animals,  such  as  the 
dog,  the  metoestrous  period  is  followed  by  a  prolonged 
period  of  rest  or  anosstrum.  In  others,  such  as  the  rat 
or  the  rabbit,  the  metcestrum  may  be  succeeded  by  only 
a  short  interval  of  quiescence.  This  short  interval, 
which  sometimes  lasts  for  only  a  few  days,  is  called  the 
dicestrum.  This  in  turn  is  followed  by  another  proces- 
trous  period,  and  so  the  cycle  is  repeated  until  the  sexual 
season  is  over.  Such  a  cycle  (consisting  of  a  succession 
of  the  four  periods,  prooestrum,  oestrum,  metoestrum,  and 
dicestrum)  is  known  as  the  dicestrous  cycle.  The  num- 
ber of  dioestrous  cycles  in  one  sexual  season  depends 
upon  the  occurrence  or  nonoccurrence  of  successful 
coition  during  oestrus.  Thus,  if  conception  takes  place 
during  the  first  oestrous  period  of  the  season,  there  can 
be  no  repetition  of  the  cycle,  at  any  rate  until  after  parturi- 
tion. The  cycle  may  then  be  repeated.  If  conception 
does  not  occur  at  any  oestrus  during  the  sexual  season, 
the  final  metoestrous  period  is  succeeded  by  a  prolonged 
anoestrous  or  non-breeding  period.  This  is  eventually  fol- 
lowed by  another  prooestrum,  marking  the  commencement 
of  a  new  sexual  season.  The  complete  cycle  of  events 
is  called  the  oestrous  cycle."  l 

56.  Puberty.  —  The  reproductive  functions  are  not  ac- 
tive in  the  young  mammal  during  its  very  early  existence. 
The  nutritive  system  during  the  same  period  is  char- 
acterized by  unusual  functional  activity  and  a  high  degree 
of  efficiency.  The  food  consumed  during  the  early  exist- 
ence of  the  mammal  produces  larger  gains  in  live  weight 
than  the  same  food  at  any  later  period  of  its  life. 

The  growth  processes  continue  to  function  with  great 

1  Marshall,  "The  Physiology  of  Reproduction,"  p.  37. 


THE   BREEDING  SEASON  57 

activity  for  a  certain  period  and  the  reproductive  organs 
gradually  develop  until  at  a  certain  age,  or  stage  of  devel- 
opment, the  essential  organs  are  matured  and  begin 
to  develop  perfect  germ-cells.  The  stage  of  develop- 
ment when  the  ovaries  of  the  female  produce  perfect 
eggs  is  called  the  period  of  puberty  and  represents  the 
beginning  of  the  breeding  season.  The  arrival  of  puberty 
in  the  female  is  accompanied  by  the  ripening  of  the  first 
ovum  or  egg  and  the  appearance  of  the  oestrum  or  heat. 
The  beginning  of  puberty  in  the  female  is  marked  by 
certain  characteristic  changes.  The  mammary  glands 
increase  in  size,  the  general  activities  of  the  body  are 
accelerated  and  the  animal  performs  certain  actions  that 
are  peculiar  to  the  period  of  the  oestrum  or  heat.  The 
coming  of  puberty  in  the  male  is  likewise  associated  with 
certain  bodily  changes  which  are  well  recognized  by  the 
practical  breeder.  In  the  stallion,  the  neck,  and  partic- 
ularly the  crest  develops,  and  the  forequarters  generally 
are  relatively  better  developed  than  the  hindquarters. 
The  most  significant  changes  however,  are  physiological. 
The  entire  system  assumes  a  state  of  greater  activity. 
Not  only  the  generative  system  is  concerned  in  this  change 
but  all  organs  and  functions  of  the  body  become  more 
active.  In  the  bull,  the  external  and  visible  changes 
are  an  enlarging  and  thickening  of  the  horns,  and  thicken- 
ing and  enlarging  of  the  neck  and  crest.  The  increased 
activity  of  males  is  indicated  by  greater  restlessness, 
irritability  and  the  development  of  a  pugnacious  tendency. 
Bulls  and  stallions  often  become  vicious  and  unmanage- 
able and  engage  in  deadly  struggles  for  supremacy. 
These  contests  are  also  common  among  the  males  of  wild 
animals.  Such  battles  have  been  observed  as  common 
among  stags  and  wild  stallions. 


58  THE   BREEDING  OF   ANIMALS 

57.  Conditions  influencing  puberty.  —  The  age  at 
which  puberty  begins  in  the  various  breeds  of  the  domestic 
animals  is  dependent  upon  the  kind  of  animal,  the 
breed,  the  food  and  general  care  of  the  young  before 
puberty.  Puberty  in  the  mare  comes  between  the  ages 
of  twelve  and  eighteen  months.  Under  normal  condi- 
tions, the  stallion  reaches  the  same  stage  at  twelve  or 
fifteen  months.  The  cow  and  bull  of  the  modern  breeds 
of  cattle  under  favorable  conditions  will  reach  this  period 
at  four  to  six  months  of  age,  but  under  ordinary  condi- 
tions, not  until  they  have  attained  the  age  of  eight  to 
twelve  months.  The  ewe  and  ram  of  the  mutton  breeds 
will  often  arrive  at  the  period  of  puberty  at  the  age  of 
five  or  six  months,  but  generally  will  require  longer. 
The  sow  and  boar  will  reach  puberty  sometimes  as  early 
as  three  months  of  age,  but  generally  at  five  to  six  months. 
The  domestic  hen  has  been  known  to  lay  eggs  at  the 
age  of  four-and-one-half  months. 

The  beginning  of  puberty  is  greatly  influenced  by  the 
nutrition  of  the  young  animal.  This  influence  begins 
with  the  foetus  in  utero.  If  the  pregnant  mother  receives 
a  generous  supply  of  nutritious  food  during  the  period 
of  gestation,  the  young  will  be  better  developed  at  birth. 
The  reproductive  system  along  with  the  other  organs  will 
have  developed  somewhat  nearer  to  the  stage  of  sexual 
completeness.  If  such  generous  nutrition  is  continued 
after  birth,  the  young  animal  will  reach  the  period  of  pu- 
berty at  an  earlier  period  than  when  fed  on  a  poorer  ration. 
At  the  Missouri  Experiment  Station,  Eckles  1  has  shown 
in  an  investigation  comparing  generous  feeding  with  a 
lighter  ration  that  the  well-fed  heifer  on  the  average  comes 
in  heat  92  days  earlier  than  those  fed  less  generously. 

1  Eckles,  "Dairy  Cattle  and  Milk  Production,"  p.  209. 


THE  BREEDING  SEASON  59 

58.  The  oestrum  and  lactation.  —  In  many  of  the 
domestic  mammals,  the  period  of  heat  is  influenced  by 
lactation.  Nursing  the  young  may  prevent  entirely  or 
retard  the  appearance  of  heat  after  parturition.  Ewes 
seldom  come  in  heat  while  suckling  young.  In  the  case 
of  cows,  the  oestrum  is  retarded.  There  is  much  varia- 
tion in  the  length  of  the  time  elapsing  between  the  birth 
of  the  young  and  the  first  appearance  of  heat  in  the  cow. 
It  is  probably  about  sixty  days,  although  it  may  recur 
earlier  or  later  than  this  period.  The  sow  will  generally 
come  in  heat  three  days  after  giving  birth  to  a  litter  of 
pigs,  but  the  oestrus  period  does  not  again  occur  until 
after  the  pigs  are  weaned.  A  prominent  breeder  of  Duroc 
Jersey  hogs,  S.  Y.  Thornton,  says,  "  In  many  cases,  a 
sow  that  is  in  good  condition  will  come  in  heat  the  third 
day  after  farrowing.  I  have  bred  them  at  that  time  but 
seldom  knew  one  to  get  with  pig  if  she  was  suckling,  but 
one  that  has  lost  her  pigs  will  invariably  get  with  pig 
from  the  first  period  which  is  usually  the  third  day  after 
farrowing.  A  sow  will  often  come  in  heat  when  her 
pigs  are  four  to  six  weeks  old  if  she  has  been  well  fed." 
The  distinguished  breeder  of  Berkshires,  A.  J.  Lovejoy, 
says,  "  Sows  often  show  signs  of  heat  on  the  third  day 
after  farrowing,  and  again  at  eight  weeks  after  farrowing, 
while  suckling.  We  find  that  after  weaning  a  litter, 
a  sow  will  usually  '  come  in '  in  three  to  five  days.'" 

The  heat  period  in  the  mare  is  very  irregular.  The 
"  foal  heat "  occurs  in  seven  to  nine  days  after  foaling. 
The  oestrum  recurs  in  most  mares  throughout  the  nursing 
period.  But  some  mares  do  not  come  in  heat  during  the 
time  they  are  suckling  foals.  It  is  a  well-known  fact 
that  there  is  a  strong  tendency  in  some  mares  to  breed 
only  once  in  two  years.  In  some  of  the  smaller  mammals, 


60  THE  BREEDING  OF  ANIMALS 

pregnancy  is  common  while  the  mothers  are  still  suckling. 
This  is  true  of  the  domestic  rabbit,  guinea  pig  and  rat.1 

59.  Heat  during  pregnancy.  —  Animals  do  not  nor- 
mally come  in  heat  during  pregnancy.     The  fertilization 
of  the  egg  of  the  female  by  the  sperm-cell  of  the  male 
sets  in  motion  a  series  of  physiological  phenomena  which 
react  upon  the  ovaries  in  such  a  way  as  to  cause  a  cessa- 
tion of  the  heat  periods.     The  ripening  of  eggs  also  does 
not  normally  occur  during  pregnancy.     There  are  excep- 
tions to  this  rule  among  certain  mammals  which  seem  to 
be  otherwise  entirely  normal. 

60.  Super!  oetation.  —  It   sometimes    happens   that   a 
pregnant  mammal  will  not  only  come  in  heat  and  exhibit 
the  various  phases  of  the  oestrum,  but  will  ripen  an  egg 
and  if  bred  to  the  male  will  conceive.     Such  an  occurrence 
is  given  the  name  of  superfoetation.     This  condition  is 
somewhat  rare,  but  has  been  observed  more  frequently 
among  mares  than  other  domestic  animals.     The  reason 
for  this  is  probably  due  to  the  fact  that  the  records  of 
breeding  are  more  carefully  kept  for  mares  than  for  cows, 
sows  or  ewes.     It  is  difficult  even  among  mares  to  deter- 
mine, when  twins  are  born,  whether  these  are  the  result 
of  one  mating  or  whether  they  may  actually  be  of  different 
ages.     Such  authentic  cases  as  are  known  have  been 
those  observed  in  the  mule-breeding  districts  of  the  United 
States.     If  the  mare  is  first  bred  to  a  stallion  and  three 
or  six  weeks  later  to  a  jack,  and  twins  are  born,  one  a 
mule  and  the  other  a  horse,  there  can  be  no  doubt  that 
these  colts  are  of  different  ages.     Such  a  result  could 
only  happen  in  mares  which  come  in  heat  and  ripen  an 
egg  during  pregnancy. 

1  Heape,  Quarterly  Journal   of  Microscopic  Science,  vol.  44, 
p.  43. 


THE   BREEDING  SEASON 


61 


61.  Examples  of  superf oetation.  —  The  literature  of 
animal-breeding  is  singularly  lacking  in  records  of  au- 
thentic cases  of  superfoetation.  The  writer  has  through 
many  years  collected  evidence  of  such  cases  in  the  mule- 
breeding  districts  of  Missouri,  and  a  few  of  these  are 
recorded  here : 

"W.  E.  Carmichael  of  Shelbyville,  Missouri,  bred  a 
mare  to  a  stallion  and  thirty  days  later  to  a  jack.  At 


FIG.  11.  —  Normal  and  usual  anterior  presentation  in  mare. 

the  end  of  the  normal  period  of  gestation  the  mare  gave 
birth  to  twins,  one  a  mule  and  the  other  a  horse  colt. 
They  were  both  dead  at  birth."  1 

A  nine^year-old  mare  belonging  to  Eugene  Rhodes  of 
Fairfax,  Missouri,  was  bred  to  a  stallion  in  May.  In 
August  she  showed  unmistakable  signs  of  heat  and  was 
mated. with  a  jack.  In  the  month  of  January  following 
she  gave  birth  to  a  perfectly  formed  mule  colt  and  a 

1  Mumford,  "Amer.  Cyclopedia  of  Agriculture,"  vol.  Ill, 
p.  31. 


62  THE   BREEDING  OF   ANIMALS 

horse  colt,  the  latter  being  considerably  shriveled  in 
appearance. 

A  case  is  reported  by  F.  K.  McGinnis  of  a  Texas  bred 
mare  belonging  to  Mr.  Carmack.  This  mare  was  bred 
several  times  to  a  stallion  during  a  period  of  six  weeks. 
She  continued  to  come  in  heat  and  the  owner,  conclud- 
ing that  she  was  sterile  with  the  stallion,  bred  her  to 
a  jack.  She  was  mated  with  the  jack  a  number  of 
times  during  a  period  of  two  weeks.  Her  owner,  finally 
despairing  of  ever  getting  the  animal  in  foal,  turned  her 
out.  At  the  end  of  eleven  months  from  the  time  the 
mare  was  first  bred  to  the  stallion  she  dropped  twin 
colts,  one  a  horse  and  the  other  a  mule.  Both  were 
dead  at  birth. 

An  interesting  example  of  superfoetation  is  recorded 
by  J.  F.  White  of  Whitesville,  Missouri,  who  bred  a  four- 
year-old  mare  to  a  saddle  stallion  on  April  25,  1909. 
She  came  in  heat  again  and  was  bred  to  a  jack  May  29, 
1909.  She  was  again  in  heat  June  12, 1909,  and  was  bred 
at  this  period  to  the  saddle  stallion  first  mentioned.  On 
May  11,  1910,  the  mare  gave  birth  to  perfectly  formed 
twin  colts.  One  of  these  was  a  mule  and  the  other  a 
horse  colt.  The  mule  died  from  illness  at  the  age  of  three 
weeks.  The  mule  colt  was  a  male.  The  horse  colt  was 
a  mare  and  developed  into  a  perfect  colt.  These  were 
the  mare's  first  colts. 

A  draft  mare  belonging  to  J.  C.  Spies  of  Newark, 
Missouri,  was  bred  to  a  jack.  Later  she  was  turned  in  a 
lot  with  her  own  two-year-old  stud  colt.  The  following 
spring  she  foaled  a  mule  and  a  horse  colt.  The  mule 
died  at  five  days  old.  The  horse  colt  lived  and  made  a 
good  horse. 

Cases  of  superfoetation  where  the  same  animal  is  the 


THE  BREEDING  SEASON  63 

sire  of  both  twins  are  probably  much  more  common  than 
is  generally  believed.  In  such  cases  it  is  difficult  to  deter- 
mine whether  the  twins  foaled  at  the  same  time  are  the 
result  of  the  fertilization  of  two  eggs  ripened  at  one  and 
the  same  heat  period,  or  whether  the  eggs  have  been  ripened 
at  different  periods  some  distance  apart. 

A  case  of  this  kind  has  been  reported  by  J.  A.  Finley 
of  Troy,  Missouri.  In  this  case  the  mare  was  bred  to  a 
jack,  and  twenty-one  days  later  she  was  found  in  heat 
again  and  was  again  bred  to  the  same  jack.  At  the  end 
of  a  few  months  she  aborted,  losing  twin  mule  colts. 
One  of  these  was  much  better  developed  than  the  other. 
It  seemed  clear  that  the  two  colts  were  from  different 
periods  of  heat,  —  in  this  instance,  twenty-one  days 
apart.1 

The  following  examples  are  probably  to  be  regarded 
as  cases  of  superfcetation :  —  A  sow  belonging  to  O. 
Young  of  Hopkins,  Missouri,  gave  birth  to  three  pigs. 
The  mother  nursed  them  for  four  or  five  days,  when  she 
weaned  them.  Three  weeks  later  the  sow  gave  birth  to 
eight  pigs,  six  of  which  lived  and  became  thrifty  young 
hogs. 

A  young  ewe  owned  by  A.  Cassity  of  Linneus,  Missouri, 
gave  birth  to  twin  lambs  on  February  13th.  About 
six  weeks  later  on  March  30th,  she  gave  birth  to  a  third 
lamb.  See  Plate  I. 

62.  Recurrence  and  duration  of  the  oestrum.  —  The 
occurrence  and  duration  of  heat  are  influenced  by  age, 
species,  food  supply,  season,  heredity  and  other  conditions. 
The  heat  period  persists  in  the  domestic  animals  for  one 
to  fifteen  days.2  The  duration  of  the  heat  period  is 

1  From  letter  to  Geo.  F.  Nardin,  dated  June  24,  1912. 

2  Hill,  "Bovine  Medicine  and  Surgery." 


64  THE   BREEDING   OF   ANIMALS 

shortest  in  the  cow  and  sheep,  being  in  these  species 
usually  from  twelve  to  twenty-four  hours.1  Mares  come 
in  heat  seven  or  nine  days  after  foaling.  Bred  at  this 
time  the  mare  is  more  certain  to  conceive.  Dimon,2 
an  experienced  horseman,  says  that  there  is  no  regular 
period  for  the  return  of  heat  in  mares.  If  mares  are  well 
fed  they  may  come  in  heat  at  any  season,  but  are  more 
generally  in  heat  in  the  spring  and  fall.3  If  the  mare 
fails  to  become  pregnant  when  bred  on  the  ninth  day 
after  foaling,  she  will  usually  be  in  heat  twenty-one  days 
thereafter.  Heat  persists  for  five  days  and  recurs  every 
twenty-one  days.4  Heat  recurs  in  the  cow  three  or  four 
weeks  after  parturition  and  recurs  every  twenty-one  days. 
The  heat  period  recurs  in  sheep  from  seventeen  to  twenty- 
five  days. 

In  the  sow  the  heat  period  will  be  observed  three 
days  after  delivery  and  usually  not  again  until  the 
pigs  are  weaned.  Heat  again  recurs  three  or  four  days 
after  weaning  the  pigs  and  every  twenty-one  days  there- 
after. 

63.  Effect  of  ration  on  recurrence  of  oestrum.  —  The 
recurrence  of  the  oestrum  after  delivery  of  the  young  is 
often  influenced  by  the  character  of  the  ration.  At  the 
Wisconsin  5  Experiment  Station,  Hart,  McCollum,  Steen- 
bock  and  Humphrey  found  that  pregnant  cows  fed  on  an 
exclusive  corn  ration  came  in  heat  in  four  to  six  weeks 
after  the  first  calf.  When  the  cows  were  fed  a  ration 

1  Weber,  "Untersuchung  fiber  die  Brunst  des  Rindes,"  Arch, 
f.  Wissensch.  u.  Prakt.  Tierheilk.,  37  Bd.,  1911. 

2  Dimon,  "American  Horses  and  Horse  Breeding." 

3  Reynolds,    "The  Breeding  and  Management  of  Draught 
Horses." 

4  Curtis,  "Cattle,  Horses,  Sheep  and  Swine." 
6  Wisconsin  Exp.  Station,  Bui.  No.  17. 


THE   BREEDING   SEASON  65 

made  up  exclusively  of  wheat  and  its  products,  the  first 
appearance  of  heat  was  from  ten  to  eighteen  weeks  after 
calving.  Fresh  pasture  also  will  often  cause  animals  to 
come  in  heat  earlier  after  delivery,  and  the  oestrum  will 
recur  with  greater  regularity. 


CHAPTER  IV 
GESTATION  AND  LACTATION 

FROM  the  time  the  egg  is  fertilized  until  the  young 
animal  is  able  to  live  an  independent  life  covers  a  period 
which  is  of  the  greatest  importance  to  the  growth  and 
development  of  the  individual  and  the  mother.  During 
this  time  all  the  physiological  activities  which  are  con- 
cerned with  growth  are  at  maximum  efficiency;  at  no 
other  period  in  the  life  of  the  animal  is  growth  so  rapid. 
Not  only  is  the  rate  of  growth  very  rapid,  but  the  food  is 
utilized  much  more  economically.  The  stage  of  develop- 
ment which  takes  place  in  the  uterus  of  the  mother  is 
the  period  of  gestation.  The  period  of  lactation  is  the 
time  during  which  the  mammalian  animal  elaborates 
milk. 

GESTATION 

64.  Indications  of  pregnancy.  —  If  the  animal  comes 
normally  in  heat  and  is  bred  to  the  male  during  the  heat 
period,  conception  occurs  in  the  natural  course  of  events 
and  pregnancy  begins  as  a  result  of  successful  conception. 
Significant  physiological  changes  occur  which  are  recog- 
nized by  the  breeder  as  evidences  of  pregnancy.  Preg- 
nant animals  do  not  normally  come  in  heat.  The  chief 
evidence,  therefore,  that  an  animal  is  "in  foal,"  "in  calf," 
"  in  pig,"  or  "in  lamb  "  is  the  cessation  of  the  periodic 
appearance  of  the  symptoms  accompanying  the  period  of 
the  oestrum.  If  after  breeding  the  mare  does  not  come  in 

66 


GESTATION   AND  LACTATION  67 

heat  for  thirty  days,  she  is  probably  safe  in  foal.  The  heat 
period  in  the  mare  persists  for  several  days,  and  therefore  a 
reappearance  of  evidences  of  heat  shortly  after  breeding 
should  not  be  regarded  as  significant.  It  is  pointed  out 
elsewhere  that  mares  may  sometimes  come  in  heat  and 
conceive  again  (see  superfcetation),  even  though  already 
pregnant.  It  is  also  true  that  some  mares  will  persistently 
refuse  the  horse,  even  though  not  pregnant.  In  the  cow 
a  period  of  sexual  quiescence  for  three  weeks  following  her 
breeding  with  the  bull  is  good  evidence  that  she  is  safely 
"  settled  "  and  in  due  time  will  give  birth  to  offspring. 

The  beginning  of  pregnancy  in  an  animal  is  often 
accompanied  by  a  marked  change  of  temperament.  A 
nervous,  excitable  mare  may  become  more  gentle  and 
docile.  It  is  also  true  that  some  mares  which  when 
not  pregnant  are  quiet  and  gentle  with  other  horses 
become  cross  during  pregnancy  and  evince  a  desire  to 
fight  other  horses.  This  tendency  increases  as  preg- 
nancy advances.  Following  conception  the  pregnant 
animal  shows  a  tendency  to  lay  on  fat  much  more  rapidly. 
Feeders  sometimes  take  advantage  of  this  tendency  to 
finish  heifers  and  sows  rapidly  for  the  market,  but  such 
a  practice  is  to  be  condemned,  as  the  meat  from  pregnant 
animals  is  less  desirable  for  human  food.  As  pregnancy 
advances,  the  abdomen  becomes  larger  at  the  sides  and 
below  and  the  flank  falls  in.  The  loins  become  depressed, 
owing  to  the  sinking  of  the  spine  due  to  the  increased 
weight  of  the  abdomen.  This  depression  of  the  loins 
gives  the  croup  bones  the  appearance  of  rising.  The 
udder  of  the  pregnant  animal  is  not  materially  changed 
during  the  initial  stages  of  gestation,  but  during  the  later 
stages  this  organ  gradually  expands  and  the  teats  become 
larger.  A  short  time  before  parturition  the  udder  be- 


68  THE   BREEDING  OF  ANIMALS 

comes  greatly  swollen  and  a  waxy  substance  exudes  from 
the  ends  of  the  teats.  In  the  cow  the  developing  foetus 
may  be  observed  externally  after  the  fifth  month  of  preg- 
nancy. If  the  cow  is  permitted  to  take  a  drink  of  very 
cold  water,  the  movements  of  the  young  calf  may  be  felt 
by  pressing  the  hand  against  the  flank  just  in  front  of 
the  stifle.  In  the  mare  the  same  movements  of  the  un- 
born foal  may  be  observed  from  the  seventh  to  the  eighth 
month  in  a  similar  manner  by  pressing  the  hand  firmly 
against  the  flank  in  front  of  the  left  stifle. 

65.  Physical  examination  for  pregnancy.  —  The  exist- 
ence of  pregnancy  may  be  determined  with  considerable 
accuracy  by  examination  through  the  rectum.  The 
method  of  making  this  examination  is  described  in  such 
an  admirable  manner  by  Law  1  that  it  is  quoted  entire : 
"  Examination  of  the  uterus  with  the  oiled  hand  intro- 
duced into  the  rectum  is  still  more  satisfactory,  and  if 
cautiously  conducted  no  more  dangerous.  The  rectum 
must  be  first  emptied  and  then  the  hand  carried  forward 
until  it  reaches  the  front  edge  of  the  pelvic  bones  below, 
and  pressed  downward  to  ascertain  the  size  and  outline 
of  the  womb.  In  the  unimpregnated  state  the  vagina 
and  womb  can  be  felt  as  a  single  rounded  tube,  dividing 
in  front  to  two  smaller  tubes  (the  horns  of  the  womb). 
In  the  pregnant  mare  not  only  the  body  of  the  womb  is 
enlarged,  but  still  more  so  one  of  the  horns  (right  or  left), 
and  on  compression  the  latter  is  found  to  contain  a  hard, 
nodular  body,  floating  in  a  liquid,  which  in  the  latter 
half  of  gestation  may  be  stimulated  by  gentle  pressure 
to  manifest  spontaneous  movements.  By  this  method  the 
presence  of  the  foetus  may  be  determined  as  early  as  the 

1  Law,  "Diseases  of  the  Horse,"  U.  S.  Department  of  Agri- 
culture, p.  155. 


GESTATION   AND  LACTATION  69 

third  month.  If  the  complete  natural  outline  of  the  virgin 
womb  cannot  be  made  out,  careful  examination  should 
always  be  made  on  the  right  and  left  side  for  the  enlarged 
horn  and  its  living  contents.  Should  there  still  be  diffi- 
culty, the  mare  should  be  placed  on  an  inclined  plane, 
with  her  hind  parts  lowest,  and  two  assistants,  standing  on 
opposite  sides  of  the  body,  should  raise  the  lower  part  of 
the  abdomen  by  a  sheet  passed  beneath  it.  Finally  the  ear 
or  stethoscope  applied  on  the  wall  of  the  abdomen  in  front 
of  the  stifle  may  detect  the  beating  of  the  foetal  heart  (one 
hundred  and  twenty-five  per  minute)  and  a  blowing  sound 
(the  uterine  sough),  much  less  rapid  and  corresponding  to 
the  number  of  the  pulse  of  the  dam.  It  is  heard  most 
satisfactorily  after  the  sixth  or  eighth  month  and  in  the 
absence  of  active  rumbling  of  the  bowels  of  the  dam." 

66.  The  period  of  gestation.  —  The  period  of  develop- 
ment from  the  fertilization  of  the  egg  by  the  sperm-cell 
until  the  birth  of  the  fully  developed  offspring  capable 
of  independent  existence  outside  the  body  of  the  mother 
is  known  as  the  period  of  gestation.  Among  oviparous 
animals  it  is  the  period  of  incubation.  This  period  varies 
greatly  as  between  different  species,  but  under  normal 
conditions  is  fairly  uniform  in  animals  belonging  to  the 
same  species.  The  normal  period  of  gestation  has  in 
general  a  more  or  less  definite  relation  to  the  size  of  the 
animal.  The  length  of  gestation  in  animals  as  reported 
by  various  authors  :  is  as  follows : 

1Nathusius,  "Zool.  Garten  Jahrg.,"  3,  1862. 

Heape,  "The  Sexual  Season,"  Quarterly  Journal  of  Micro- 
scopical Science,  vol.  44,  1900. 

Ewart,  "The  Development  of  the  Horse,"  Quarterly  Journal 
of  Microscopical  Science. 

Wortley  Axe,  "The  Mare  and  the  Foal,"  Journal  of  the  Royal 
Agricultural  Society,  3d  series,  vol.  IX,  1898. 


70        THE  BREEDING  OF  ANIMALS 

Elephant 20  to  23  months 

Giraffe 14  months 

Dromedary 12  months 

Buffalo .  10  to  12  months 

Camel 13  months 

Jennet  .     . 12  months 

Seal 11  to  12  months 

Mare 11  to  12  months 

Zebra  and  Celtic  Pony     .     .     .     .  334  to  338  days 

Prjewalsky's  Horse 356  to  359  days 

Cow 9  months 

Bear 6  months 

Reindeer 8  months 

Monkeys 7  months 

Sheep  and  Goat 21  to  22  weeks 

Sow 4  months 

Lion 3^  months 

Dog 59  to  63  days 

Fox  and  Wolf 63  to  63  days 

Guinea  Pig 61  days 

Cat 63  days 

Polecat 40  days 

Rabbit .     .  30  days 

Squirrel  and  Rat 28  days 

Mice 21  days 

Small  breeds  require  a  shorter  time  than  larger  breeds, 
but  this  influence  may  be  overcome  in  breeds  which  have 
long  been  selected  for  early  maturity.  According  to 
Youatt,1  all  domestic  animals  are  subject  to  considerable 
variation  in  the  length  of  gestation  both  above  and  below 
the  normal  period.  Tessier 2  has  observed  a  large  num- 
ber of  pregnant  females  among  the  domestic  animals 
and  has  reported  marked  variations  in  the  time  required 
for  complete  development  of  the  foetus  and  final  expul- 
sion from  the  uterus.  This  authority  has  reported  on 
582  mares  in  which  the  period  of  gestation  ranged  from 

1  Youatt,  "Cattle,"  p.  521. 

2  Tessier,  "Recherches  sur  la  Duree  de  la  Gestation,"  Mem. 
de  1'Acad.  des  Science,  Paris,  1817. 


GESTATION   AND  LACTATION 


71 


287  to  419  days.  Among  1131  cows  the  length  of  the 
period  varied  from  240  to  321  days.  The  minimum  gesta- 
tion period  among  912  sheep  was  146  days  and  the  maxi- 
mum 161  days.  It  is  of  interest  to  note,  however,  that 
among  676  ewes  the  period  varied  from  150  to  154  days 
only. 

The  Earl  of  Spencer  1  found  the  period  to  vary  from 
220  to  313  days  in  cows.  The  following  table  includes 
the  observations  of  a  number  of  investigators  and  is  useful 
as  indicating  the  somewhat  wide  variations  which  may 
occur  in  the  gestation  period  of  the  domestic  animals : 

PERIOD  OF  GESTATION  IN  DOMESTIC  ANIMALS  2 


NUMBER  OP 
CASES 

MAXIMUM 
DAYS 

MINIMUM 
DAYS 

AUTHORITY 

Mares    
Mares    
Cows      
Cows     
Cows     
Cows     

582 

25 

575 
764 
50 
98 

419 

367 
299 
285 
291 
299 

287 
324 
240 
220 
268 
276 

Tessier 
Gayot 
Tessier 
Spencer 
Allen 
Bement 

Cows     
Ewes     .     .     . 
Ewes      
Sows      
Sows      

182 
912 
420 
25 
10 

296 
161 
156 
123 
116 

280 
146 
143 
109 
101 

Wing 
Tessier 
Magne 
Tessier 
Fox 

1  Journal  of  the  Royal  Agricultural  Society,  vol.  I,  pp.  166,  167. 

2  See  Tessier,  Journal  of  the  Royal  Agricultural  Society,  vol.  I, 
pp.  166,  167. 

Franck-Albrecht-Goring,  "  Die  Trachtigkeitsdauer,"  Thier- 
artzliche  Geburtshiilfe,  vol.  4,  1901. 

Wing,  Cornell  Experiment  Station,  Bui.  162. 
Smith,  "Physiology  of  the  Domestic  Animals." 
Allen,  "American  Cattle,"  p.  259. 
Miles,  "Stock  Breeding,"  1907,  p.  400  et  seq. 


72  THE  BREEDING  OF  ANIMALS 

The  period  of  gestation  in  the  domestic  jennet  is 
370  days.  Careful  records  kept  by  Kalo  Monsees 1 
on  the  large  jack-  and  jennett-breeding  farm  of  Monsees 
and  Sons  at  Smithton,  Missouri,  indicates  that  the  maxi- 
mum gestation  period  for  a  living  colt  was  13  months 
and  16  days.  The  minimum  period  was  11  months  and 
15  days.  The  average  period  was  370  days.  These 
figures  may  be  taken  as  reliable  since  they  cover  a  large 
number  of  animals  of  varying  ages  and  sizes  for  several 
years  and  represent  the  progeny  of  different  jacks. 

67.  Causes  of  variation  in  length  of  gestation  period.  — 
The  causes  of  variations  in  the  time  required  for  the 
development  of  the  young  in  the  uterus  are  not  always 
clearly  apparent.  It  is  probable  that  prolonged  gesta- 
tion may  sometimes  be  due  to  the  mother  suckling  young 
during  pregnancy,  resulting  in  providing  an  insufficient 
supply  of  food  to  the  developing  fretus.2  Tesster  con- 
cludes that  the  length  of  the  period  of  gestation  does 
not  depend  upon  age,  constitution  of  the  female,  diet, 
breed  or  season.  Nathusius 3  and  others  have  found 
that  comparing  races  and  breeds  belonging  to  the  same 
species,  those  which  have  been  selected  for  their  early 
maturing  qualities  have  a  shorter  gestation  period. 
Darwin 4  has  given  some  evidence  of  this  in  connection 
with  the  .grading  up  of  Merino  sheep  bred  to  the  earlier 
maturing  Southdown.  The  length  of  gestation  is  given 
as  follows : 

1  Kalo  Monsees,  "Breeding  Records  of  Monsees  and  Sons  Jack 
and  Jennet t  Breeding  Farm." 

2  Pinard,  "Gestation,"  Richets  Dictionnaire  de  Physiologie, 
vol.  7,  Paris,  1905. 

3  Loc.  cit.  ' 

4  Darwin,  "Animals  and  Plants  under  Domestication,"  vol. 
1,  p.  123. 


GESTATION   AND  LACTATION  73 

Merinos ,     *     .  .  150.3  days 

Southdowns .  144.2  days 

Half  blood  Merino  and  Southdown   .  .  146.3  days 

Three  quarter  blood  Southdown  .     .  .  145.5  days 

Seven  eighths  blood  Southdown    .     .  .  144.2  days 

Some  doubt  has  been  expressed  as  to  the  authenticity 
of  the  maximum  period  of  gestation  in  mares.  The  edi- 
tor of  the  Breeder's  Gazette  eommenting  on  this  fact  says, 
"Mares  are  usually  credited  with  pregnancy  lasting  eleven 
months.  When  they  run  twelve  months  we  prefer  to 
believe  that  the  date  has  not  been  properly  kept.  We 
believe  that  forty-eight  weeks,  seven  days  to  the  week,  or 
326  days  is  about  the  average  duration  of  pregnancy  in 
a  mare."  1  Referring  to  this  statement  M.  W.  Johnson  2 
of  Illinois  writes  that  he  has  been  in  the  breeding  business 
for  fourteen  years  and  has  complete  records  on  the  breed- 
ing of  5000  mares.  He  reports  one  mare  as  having  carried 
her  foal  for  twelve  months  and  sixteen  days  and  another 
for  twelve  months  and  eighteen  days.  Both  foals  were 
deformed.  Another  mare  gave  birth  to  a  perfectly 
healthy  foal  at  the  end  of  one  year  and  eighteen  days  while 
another  carried  her  foal  exactly  thirteen  months  and 
dropped  a  healthy  foal.  A  Percheron  mare  belonging  to 
H.  F.  Sperry  3  dropped  a  mule  colt  twelve  months  and 
two  days  after  breeding.  William  Lokings  of  South 
Dakota  owned  a  pony  mare  which  was  twice  bred  and 
gave  birth  to  a  foal  twelve  months  and  twenty-five  days 
after  the  last  service.  There  is  a  popular  belief  that 
male  offspring  are  carried  longer  than  female.  Bement  4 
found  that  the  average  length  of  gestation  for  male  calves 

1  Breeder's  Gazette,  May  15,  1907. 

2  Ibid.,  June  19,  1907. 

3  Ibid.,  June  26,  1907. 

4  The  Cultivator,  1845,  p.  207. 


74  THE   BREEDING   OF  ANIMALS 

was  288  days  and  for  females  283  days,  but  in  1839  the 
female  calves  were  carried  longer  than  the  males.  Earl 
Spencer  1  also  believed  there  was  some  relation  between 
sex  and  the  length  of  gestation.  M.  Magne  2  found  the 
period  of  gestation  longer  "for  ewe  lambs  than  for  ram 
lambs.  C.  U.  Connellee  3  of  Texas  finds  no  relation  be- 
tween the  sex  of  foals  and  the  time  required  for  gestation. 
The  evidence  available  is  insufficient  to  justify  the  belief 
that  male  offspring  are  carried  longer  than  females. 

68.  Incubation.  —  The  period  of  incubation  in  fowls 
represents  in  oviparous  animals  the  phenomenon  of  gesta- 
tion in  mammals.  The  length  of  the  period  of  incubation 
among  domestic  birds  is  given  by  Miles  4  as  follows : 

"  Turkey,  twenty-six  to  thirty  days ;  guinea  hen, 
twenty-five  to  twenty-six  days;  pea-hen,  twenty-eight 
to  thirty  days;  ducks,  twenty-five  to  thirty-two  days; 
geese,  twenty-seven  to  thirty-three  days ;  hens,  nineteen 
to  twenty-four  days,  or  an  average  of  twenty-one ;  pigeons, 
sixteen  to  twenty  days;  canary-birds,  thirteen  to  four- 
teen days.  Mr.  Wright  remarks  that  '  cold  weather,  or 
a  prevailing  east  wind,  will  lengthen  the  time  a  day  or 
more,  while  warm  weather  and  an  attentive  sitter  will 
hasten  it ;  stale  eggs  also  hatch  later  than  fresh/  ' 

The  smaller  breeds,  like  bantams,  hatch  in  nineteen 
or  twenty  days,  while  the  heavier  breeds  may  require 
as  long  as  twenty-two  days  for  complete  incubation. 
When  eggs  are  artificially  incubated,  it  has  been  found 
that  a  higher  temperature  combined  with  favorable 
moisture  conditions  will  shorten  the  period. 

1  Spencer,  Journal  of  the  Royal  Agricultural  Society,  vol.  1, 
p.  168.  2  Loc.  cit. 

3  Breeder's  Gazette,  June  26,  1907. 

4  Miles,  "Stock  Breeding,"  p.  401. 


GESTATION   AND   LACTATION  75 

69.  Parturition.  —  In  mammalian  animals  at  the  end 
of  the  period  of  gestation  and  in  the  normal  course  of 
events,  the  fully  developed  foetus  is  expelled  from  the 
uterus.  This  phenomenon  is  known  as  parturition.  The 
beginnings  of  parturition  are  accompanied  by  a  series 
of  rhythmic  contractions  (labor  pains)  of  the  uterus  which 
eventually  result  in  the  birth  of  the  offspring.  These 
contractions  are  at  first  partially  controlled  by  the  will, 
but  later  are  entirely  involuntary.  That  the  muscular 
movements  of  the  uterus  are  not  controlled  entirely  by 
the  central  nervous  system  is  shown  by  the  researches 
of  Kehrer,1  Helme  and  others.  These  investigators  found 
that  a  healthy  uterus  may  rhythmically  contract  when 
separated  from  the  body  if  it  is  maintained  at  body  tem- 
perature without  important  variations.  The  powerful 
muscular  contractions  of  the  uterus  of  mammals  are 
characterized  by  the  mechanical  stretching  of  the  bag  of 
membranes  by  severe  contraction  of  the  longitudinal 
muscle  fibers  and  the  relaxation  of  the  circular  fibers  of 
the  cervix.  The  contraction  of  the  uterus  and  the  relaxa- 
tion of  the  cervix  causes  the  bag  of  membranes  to  act  as 
a  fluid  wedge  still  further  extending  the  neck  of  the 
womb.  These  phenomena  are  followed  by  the  head  and 
fore  legs  of  the  young  animal,  the  rhythmic  contractions 
become  more  frequent  and  more  powerfully  exerted,  and 
these  are  supplemented  by  the  abdominal  muscles  in 
the  final  stages  of  parturition.  The  immediate  inciting 
causes  of  parturition  are  not  well  known.  Various 
explanations  have  been  attempted.  Spiegelberg 2  has 
suggested  that  the  foetus  secretes  a  substance  which 

1  Marshall,  "  The  Physiology  of  Reproduction,"  p.  527. 

2  Spiegelberg,  ''Die  Dauer  der  Geburt,"  Lehrbuch der  Geburts- 
hiilfe,  vol.  II,  1891. 


76  THE   BREEDING  OF  ANIMALS 

finally  entering  the  maternal  blood  reaches  the  nerve 
centers  and  through  them  acts  on  the  uterine  nerves 
in  the  spinal  cord.  Beard 1  and  others  have  held 
that  there  is  an  intimate  relation  between  the  oestrus 
cycle  and  parturition.  It  is  known  that  abortion  is 
more  apt  to  occur  at  the  time  of  the  periodical  return  of 
heat.  But  may  it  not  be  true  that  the  period  of  gesta- 
tion is  itself  governed  by  a  certain  rhythmic  law  or  peri- 
odicity similar  to  that  which  brings  about  the  heat  period  ? 
Other  possible  explanations  are  that  the  placenta  begins 
to  decay  or  atrophy  at  the  end  of  a  given  period  and  thus 
loses  its  hold  on  the  uterine  walls,  and  the  waste  products 
thus  developed  may  furnish  the  real  stimulus  which 
results  in  parturition.2  The  death  of  the  foetus  prema- 
turely will  generally  bring  on  expulsive  movements  of 
the  uterus  and  speedily  relieve  the  uterus  of  its  dead 
burden. 

It  is  probable  that  the  causes  of  parturition  are  very 
complex  and  that  a  combination  of  the  above,  together 
with  other  causes,  may  bring  about  eventually  the  suc- 
cessful birth  of  the  young  mammal  after  the  normal 
period  of  existence  in  the  uterus.3 

70.  Normal  parturition  of  the  domestic  animals.  — 
Under  ordinary  conditions  and  in  due  course  of  time,  the 
young  of  the  domestic  animals  are  born  without  diffi- 
culty. When  difficult  parturition  occurs,  it  may  be  due 
to  mal-presentation  of  the  foetus,  malformation  of  the 
foetus,  malformation  of  the  mother,  or  disease  of  the  mother 
preventing  the  normal  expulsion  of  the  foetus. 

1  Beard,  "The  Span  of  Gestation  and  the  Cause  of  Birth," 
Jena,  1887. 

2 Williams,  "Obstetrics,"  London,  1904. 
3  See  also  Marshall,  loc.  cit. 


GESTATION   AND   LACTATION 


77 


71.  Mai-presentations.  —  In  order  that  the  offspring 
may  be  successfully  expelled  from  the  generative  organs 
of  the  mother,  it  is  necessary  that  it  should  approach 
the  neck  of  the  uterus'in  a  certain  form  or  "  presentation." 
In  all  the  mammalian  domestic  animals  the  normal  pres- 
entation is  one  in  which  the  fore  legs  are  extended  for- 
ward with  the  nose  also  extended  forward  and  lying 
between  the  knees.  (See  Fig.  11.)  In  case  of  twins, 


FIG.  12.  —  Parturition  in  mare.  Posterior  presentation. 

the  second  is  generally  presented  with  the  hind  feet  first. 
(See  Fig.  12.)  Any  other  presentation  than  the  two  here 
described  is  abnormal,  and  the  birth  of  young  under  such 
conditions  is  difficult  or  impossible. 

As  most  cases  of  difficult  parturition  are  due  to  abnormal 
presentations,  it  is  important  that  the  more  common 
mal-presentations  should  be  mentioned.  The  more  com- 
mon and  difficult  mal-presentations  are  :  —  head  normal, 
but  fore  legs  bent  back  at  the  knee  (Fig.  13) ;  head  normal, 
but  fore  legs  bent  back  from  the  shoulders  and  entirely 


78 


THE   BREEDING   OF  ANIMALS 


FIG.  13.  —  Abnormal    anterior 
tation. 


presen- 


under  the  body ;  fore  feet  normal,  but  head  bent  to  one 
side  or  downward ;  fore  legs  normal,  but  the  head  bent 
backward  and  upward ;  all  four  feet  presented ;  thigh 
and  croup  presented  first,  with  hind  legs  bent  under 

body  (Fig.  14) ;  the  back 
first  presented,  with  fore 
and  hind  legs  extending 
backward  toward  the 
uterus  (Fig.  15). 

72.  Normal  presen- 
tations. —  In  the  early 
stages  of  parturition, 
it  is  desirable  to  deter- 
mine whether  the  foetus 
is  normally  in  position 
to  be  expelled  with  least 

difficulty.  As  already  described,  the  normal  presenta- 
tion is  head  and  fore  legs  forward,  or  in  some  cases 
(twins)  the  hind  legs  forward.  In  making  the  examina- 
tion for  the  purpose  of  determining  whether  the  foetus  is 
in  proper  position,  the  hand  and  arm  should  be  thoroughly 
cleansed  and  oiled 
with  vaseline,  and 
inserted  into  the 
vagina  and  an  ex- 
amination made. 
The  manipulation 
should  be  conducted 
with  extreme  gentle- 
ness and  under  such  conditions  as  shall  not  excite  the 
pregnant  animal.  Advantage  should  be  taken  of  the 
lulls  in  the  labor  pains  to  make  the  examinations.  While 
the  muscular  contractions  are  on  in  full  force,  little  can 


FIG.  14.  —  Abnormal  posterior  presentation. 


GESTATION   AND   LACTATION 


79 


be  accomplished.  If  the  foetus"  is  found  to  be  normally 
presented,  it  is  always  wise  to  let  nature  take  her  course, 
and  in  most  cases  birth  ensues  without  assistance  from 
the  attendant. 

73.  Treatment  for  mal-presentation.  —  If  the  exam- 
ination reveals  the  fact  that  the  foetus  is  not  normally 
presented,  an  effort  should  be  made  to  readjust  the 


FIG.  15.  —  Abnormal  transverse  presentation. 

unborn  animal  so  that  it  will  be  normally  presented. 
In  the  case  of  valuable  breeding  animals,  it  is  generally 
best  to  secure  at  once  the  services  of  a  skilled  veterinarian. 
In  attempting  to  make  the  readjustment  of  the  foetus, 
the  same  care  and  gentleness  should  be  exercised  as  in 
the  initial  examination.  In  order  that  the  mal-presenta- 
tion may  be  successfully  adjusted  and  the  fore  legs  and 
head  properly  brought  forward  into  the  cervix  and  vagina, 
it  will  be  necessary  to  push  the  foetus  back  into  the  uterus 
where  there  will  be  sufficient  room  for  the  manipulation. 


80  THE   BREEDING   OF  ANIMALS 

If  the  labor  pains  have  already  proceeded  for  some  time, 
it  may  at  first  be  found  somewhat  difficult  to  return  the 
foetus  to  the  uterus.  In  all  cases  it  will  be  useless  to 
attempt  to  push  back  the  unborn  animal  during  the  severe 
labor  pains.  But  as  the  resting  period  and  consequent 
relaxation  follow  each  severe  contraction,  the  foetus  may 
be  gradually  pushed  back.  It  is  sometimes  helpful  par- 
tially to  suspend  the  hind  quarters  of  the  pregnant  mother 
by  roping  the  feet  and  hoisting  the  hind  quarters  so  that 
they  will  be  somewhat  higher  than  the  forequarters,  and 
in  this  position  it  is  generally  easier  to  accomplish  the 
return  and  readjustment.  In  most  cases  in  which  the 
foetus  and  mother  are  in  normal  health  and  condition, 
the  foetus  may  be  expelled  without  great  difficulty  after 
readjustment,  that  is,  provided  the  mother  has  not 
become  too  severely  exhausted  by  long-continued  labor. 
In  such  case  it  is  necessary  to  render  aid  by  supplement- 
ing the  mother  in  her  efforts  to  expel  the  foetus.1 

LACTATION 

The  young  of  most  mammalian  animals  are  born  into 
the  world  in  an  immature  and  often  quite  helpless  condi- 
tion. In  most  species  the  newborn  animal  is  unfit  to 
live  and  thrive  independently.  In  particular  the  nutri- 
tive functions  of  the  very  young  mammal  are  not 
developed  to  a  point  where  the  individual  can  immedi- 
ately exist  on  the  food  consumed  by  the  mature  parent. 
To  provide  nourishment  for  the  very  young  animal,  all 
mammals  are  provided  with  mammary  glands  which 
secrete  milk. 

JSee  Law,  "  Diseases  of  Cattle,"  1908,  and  "  Diseases  of  the 
Horse,"  1907,  U.  S.  Department  of  Agriculture. 


GESTATION   AND   LACTATION  81 

74.  The  mammary  glands.  —  All  mammals  are  supplied 
with  milk-secreting  glands.     These  glands  are  present 
in  both  sexes,  but  are  rudimentary  in  the  male.     In  the 
female  the  glands  are  large  and  are  stimulated  into  active 
functioning  by  the  exercise  of  the  reproductive  organs. 
In  the  immature  female  before  the  arrival  of  puberty, 
these   glands   are   small   and   inconspicuous.     With  the 
first  appearance  of  puberty  accompanied  by  the  oestrum, 
the  glands  increase  in  size. 

The  number  of  glands  present  varies  with  the  species. 
In  some  animals  which  normally  give  birth  to  one  offspring 
at  a  time,  as  in  man,  there  are  two  glands  (mammae). 
In  the  cow,  however,  normally  producing  one  at  a  birth, 
the  normal  number  of  mammae  is  four.  In  cats,  dogs, 
rabbits  and  swine,  species  producing  from  four  to  twenty 
young  at  one  time,  there  are  normally  present  several 
pairs  of  mammae.  Wentworth  found  the  number  of 
mammae  in  swine  to  vary  from  nine  to  fourteen.1  There 
is,  therefore,  a  rather  definite  relation  between  the  num- 
ber of  mammae  and  the  normal  number  of  young  pro- 
duced at  each  birth.  This  relation  does  not  seem  to  be 
important  as  an  index  of  fertility  in  any  particular  species. 

75.  The  duration  of  lactation.  —  Among  wild  forms  the 
continuance  of  lactation  varies  widely  in  different  species. 
In  general  the  period  of  lactation  ends  when  the  young 
animal  has  developed  to  a  point  where  it  can  live  in- 
dependently and  secure  its  nourishment  in  the  same  way  as 
thejnature  individual.     In  the  case  of  the  domestic  cow, 
the  milking  function  has  been  developed  and  stimulated 
under  domestication  to  a  point  where  the  lactation  period 
may  persist  from  one  calving  period  to  the  next  without 

1  Wentworth,  "Inheritance  of  Mammae  in  Duroc- Jersey 
Swine,"  American  Naturalist,  vol.  47,  1913. 


82  THE   BREEDING  OF  ANIMALS 

intermission.  The  more  important  conditions  which  in- 
fluence the  duration  of  lactation  and  the  amount  of  milk 
produced  among  the  domestic  animals  are  food  supply, 
habit,  heredity,  exercise,  climate  and  nervous  excitement. 

76.  The  food  supply.  —  Every  mature  domestic  animal 
requires  a  certain  minimum  amount  of  food  to  maintain 
the  ordinary  bodily  functions.     This  is  called  the  food 
of  maintenance.     The  function  of  milk-giving  must  be 
regarded    as    an    additional    requirement.     The    animal, 
therefore,   that   is   producing   milk   must   consume   and 
assimilate  larger  quantities  of  food  than  one  that  is  dry 
or  not  producing  milk.     It  follows  that  the  greater  the 
amount  of  milk  produced,  the  larger  the  demands  of  the 
lactating  animal  for  food.     In  an  ordinary  cow  in  full 
milk,  the  food  of  maintenance  may  represent  sixty  per 
cent  of  all  the  food  eaten.     In  this  case  forty  per  cent 
of  the  ration  is  available  for  milk  production.     In  a 
heavy-producing    cow,    the    food    of    maintenance    may 
represent  only  forty  per  cent  of  the  whole.     In  the  latter 
case,  as  much  as  sixty  per  cent  of  the  ration  may  be  utilized 
for  milk  production.     The  greater  economy  of  production 
in  the  case  of  the  heavy-producing  cows  is  at  once  appar- 
ent.    If  an  insufficient  ration  is  fed  to  any  cow  in  full 
milk,  the  first  effect  will  be  to  cut  down  the  milk  flow. 

77.  Habit.  —  The  duration  of  the  lactation  period  is 
materially  influenced  by  the  habit  of  the  cow  as  deter- 
mined by  man.     The  lactation  period  of  a  cow,  which  is 
normally  ten  months,  may  be  shortened  by  careless  milk- 
ing or  insufficient  feeding.     The  milking  function  may  be 
so  stimulated  by  careful  and  thorough  milking  and  intelli- 
gent feeding  that  the  daily  quantity  of  milk  may  be 
increased  and  the  period  of  lactation  lengthened. 

78.  Heredity. — The  capacity  to  give  milk  in  abundance 


GESTATION  AND  LACTATION  83 

is  hereditary.  The  present  highly  productive  dairy  breeds 
owe  their  greater  ability  to  produce  large  quantities  of  milk 
to  their  inheritance  of  this  quality  from  their  ancestors. 
In  the  same  breed  certain  families  are  known  to  possess  the 
quality  of  large  capacity  for  milk  production  to  a  higher  de- 
gree than  the  average  of  the  breed.  It  is  also  true  that  the 
duration  of  the  period  of  lactation  is  influenced  by  heredity. 

79.  Exercise.  —  An    excessive    amount    of    muscular 
exertion  of  any  kind  must  be  regarded  as  unfavorable 
to  the  maximum  production  of  milk.     Cows  that  are 
required  to  travel  long  distances  over  sparse  pastures 
in  order  to  secure  sufficient  food  for  their  needs  cannot 
produce   their   maximum   quantity   of   milk.     In   many 
European    countries,    cows    are    generally    employed    as 
draft  animals  in  the  ordinary  farm  operations  of  plowing, 
harrowing,  reaping  and  other  work.     Investigations  in 
Germany  have  shown  that  so  long  as  cows  are  employed 
at  moderate  work  the  milk  flow  is  not  decreased.     When- 
ever cows  were  compelled  to  work  at  heavy  labor  and 
for  long  hours,  invariably  the  flow  of  milk  was  decreased. 

80.  Climate.  —  Exposure  to  extreme  dry  cold  or  to  cold 
driving  storms  will  have  the  effect  of  decreasing  the  normal 
milk  yield  of  a  herd  of  cows.     In  general,  a  lack  of  ade- 
quate shelter  in  a  cold  and  humid  climate  may  seriously  in- 
terfere with  the  highest  development  of  the  milking  func- 
tions.    A  herd  of  cows  will  produce  more  milk  in  winter 
if  provided  with  water  which  has  been  slightly  warmed. 

81.  Unusual  lactation.  —  In  general,  lactation  is  closely 
associated   with   reproduction.     Pregnancy   followed   by 
parturition  normally  precedes  the  secretion  of  milk  in 
the  mammary  glands.     Males  and  sterile  females  possess 
rudimentary  mammae  but  seldom  secrete  milk,  although 
a  number  of  cases  are  on  record  where  males  have  been 


84 


THE  BREEDING  OF  ANIMALS 


known  to  secrete  milk.  The  hybrid  mare  mule  in  rare 
cases  has  been  known  to  secrete  milk  through  the  excita- 
tion of  the  mammary  glands.  In  the  cases  observed, 
the  mammary  glands  have  generally  been  stimulated 
to  secrete  through  the  persistent  suckling  of  some  young 
mule  colt  which  may  have  been  running  in  the  same 
pasture  or  lot.  It  is  rare  that  the  mammary  glands  of  a 
mare  mule  will  develop  to  the  point  of  secreting  milk 
in  the  absence  of  some  such  stimulation. 

The  author  has  discovered  one  mare  mule  which  has 
secreted  milk  without  any  such  stimulus.  This  mare 
mule  belonging  to  L.  O.  Swarner  of  Boonville,  Missouri, 
when  first  observed  had  been  giving  milk  for  some  weeks. 
The  owner  in  a  letter  to  the  author  says :  "I  have  a  mule 
that  has  been  giving  milk  the  same  as  a  brood  mare  does 
when  suckling  a  colt.  She  has  been  giving  milk  for  about 
five  weeks.  The  mule  is  still  giving  milk,  as  much  as  a 
quart  at  a  time.  (See  Plate  III,  upper.)  The  milk  is  pure 
white  and  streams  from  her  udder."  This  mare  mule 
came  in  heat  regularly  and  was  bred  several  times  but 
failed  to  become  pregnant.  The  milk  was  analyzed  by 
the  Missouri  Experiment  Station.  The  analysis  is  shown 
in  the  table  in  comparison  with  cow's  and  human  milk : 

COMPOSITION   OP  MILK  FROM   MARE   MULE    COMPARED  WITH 
Cow's  AND  HUMAN  MILK 


MAKE  MULE 
"BECK" 

Cow's  MILK 

HUMAN  MILK 

Water             .     .     .     .     . 

90.441% 

87  17% 

87.41  % 

Total  Solids   .     .     .    '.    » 

9.559 

12.83 

12.59 

Ash                                .     . 

0400 

071 

.31 

Fat        

1.450 

3.64 

3.78 

Protein                           •. 

2  463 

3  55 

2.29 

Sugar 

5.792 

4.88 

6.21 

PLATE   III.  —  Upper.     A  mare  mule  that  gives  milk.     Lower.     A 
Free-Martin  heifer  that  proved  fertile. 


CHAPTER  V 
FERTILITY 

THE  larger  number  of  the  breeders  of  domestic  animals 
are  engaged  merely  in  the  multiplication  of  animals. 
They  are  not  primarily  striving  for  the  improvement  of 
the  species.  To  all  these,  the  ability  of  an  animal  to 
produce  young  in  abundance  is  of  fundamental  impor- 
tance. To  the  relatively  small  class  of  breeders  who  are 
successful  in  really  improving  the  desirable  characteristics 
of  existing  breeds,  the  quality  of  fertility  is  likewise  of 
primary  importance.  When  the  breeder  has  succeeded 
in  developing  a  highly  improved  strain,  it  becomes  im- 
portant to  secure  as  many  offspring  possessing  the  new 
and  desirable  qualities  as  possible. 

Fertility  may  be  defined  as  the  ability  of  an  animal 
to  produce  young  in  abundance.  This  quality  depends 
upon  the  number  of  young  born  at  one  time,  the  fre- 
quency of  the  recurrence  of  the  oestrum,  the  duration  of 
the  period  of  gestation,  and  the  length  of  the  period  of 
life  during  which  reproduction  occurs.  All  of  the  above 
conditions  are  affected  by  many  circumstances,  some 
external,  others  internal  and  inherent  in  the  individual 
and  the  species.  Many  of  the  circumstances  influencing 
fertility  can  be  directly  or  indirectly  controlled  by  man, 
others  are  beyond  his  control. 

82.  The  number  of  young  at  a  birth.  —  There  is  very 
great  variation  among  animals  in  respect  to  the  number 

85 


86  THE   BREEDING   OF   ANIMALS 

of  young  born  at  one  birth.  This  difference  is  very 
marked,  as  between  different  species,  for  example,  as 
between  the  sow  and  the  ewe.  A  similar  difference  is 
likewise  to  be  observed  between  individuals  and  families 
belonging  to  the  same  species.  In  a  general  way,  the 
number  of  young  carried  in  the  uterus  at  one  time  seems 
to  depend  upon  the  size  of  the  animal.  Thus  the  ele- 
phant, rhinoceros,  hippopotamus,  giraffe,  bison,  domes- 
tic mare  and  cow,  produce  one  young  at  a  birth.  The 
goat  and  sheep,  while  normally  producing  one  offspring 
at  a  time,  may  frequently  produce  twins  and  triplets  or 
even  a  larger  number  at  one  birth. 

The  hare  and  rabbit  are  much  smaller  than  the  sheep 
and  are  very  much  more  prolific.  The  wild  rabbit  pro- 
duces from  four  to  eight  in  a  litter.  The  domestic  rabbit 
is  more  prolific  than  the  wild,  often  giving  birth  to  eight 
or  ten  at  one  time. 

The  lion  and  tiger  in  a  wild  state  give  birth  to  two  to 
three  cubs,  while  the  domestic  cat  will  sometimes  produce 
as  many  as  nine.  The  size  of  the  litter  in  the  fox  is  from 
four  to  eight.  The  number  of  young  in  the  litter  of  the 
domestic  dog  varies  from  five  to  twelve. 

The  domestic  sow  is  an  exception  to  the  general, rule 
that  smaller  species  are  more  prolific.  The  sow  is  the 
most  prolific  of  the  more  important  domestic  animals, 
though  not  the  smallest.  The  wild  sow's  litter  numbers 
four  or  five.  The  domestic  sow  produces  from  seven  to 
twelve,  and  much  larger  litters  are  common. 

The  smaller  rodents,  like  the  rat  and  mouse,  are  char- 
acterized by  large  litters.  The  rat  regularly  gives  birth 
to  twelve  or  fifteen  young  at  a  time  and  has  been  known 
to  produce  twenty  at  one  birth.  The  mouse  is  equally 
prolific. 


FERTILITY  87 

It  does  not  seem  to  be  generally  true  among  domestic 
animals  that  the  smaller  breeds  are  more  fertile  than  the 
larger  breeds  of  the  same  species.  Among  sheep,  the 
American  Merino  and  Southdown  are  relatively  small 
breeds,  but  are  less  prolific  than  the  larger  Shropshire, 
Cotswold  or  Lincoln.  The  smaller  breeds  of  swine, 
like  the  Essex,  Cheshire  and  Small  Yorkshire,  are  in 
general  less  prolific  than  the  larger  Berkshire,  Duroc- 
Jersey  and  Large  Yorkshire.  In  this  instance,  it  is 
probable  that  selection  by  man  has  intervened  to  counter- 
act the  general  law  that  the  smaller  animals  are  more 
fecund. 

83.  Period  of  gestation  and  fertility.  —  The  length  of 
the  period  of  gestation  seems  to  be  some  index  of  the 
number  of  young  produced  at  a  birth.  In  all  animals 
requiring  a  longer  period  of  gestation  than  six  months, 
one  is  the  normal  number  of  young  at  a  birth.1  Among 
the  animals  in  which  the  period  is  less  than  six  months 
are  the  hog,  sheep,  goat,  rabbit,  dog,  cat,  rat  and  mouse. 
In  all  of  these,  except  the  sheep  and  goat,  the  normal 
number  is  greater  than  one.  The  sheep  and  goat  under 
domestication  have  so  increased  in  fertility,  in  the  cases 
of  some  breeds  at  least,  that  fecundity  is  much  greater 
than  in  the  horse  or  cow,  where  single  births  are  the  rule. 
Milch  goats  usually  drop  twins,  and  triplets  are  not  rare.2 

The  Border  Leicester  breed  in  England  has -produced 
150  to  160  per  cent  of  lambs  under  ordinary  conditions. 
When  the  same  breed  has  been  specially  fed  before  breed- 
ing, the  number  of  lambs  has  been  increased  to  200  per 
cent. 

1  Marshall,  "The  Physiology  of  Reproduction." 
2Clos,    vol.    Ill,   p.   410,    "Cyclopedia   of   American   Agri- 
culture." 


88  THE  BREEDING   OF  ANIMALS 

84.  Fertility  and  the  frequency  of  the  recurrence  of  the 
oestrum.  —  The    fertility  of  animals  is  also  dependent 
upon  the  frequency  of    the  recurrence  of  the  oestrum. 
As  already  described,  the   recurrence    of   heat  depends 
upon    a    number    of    conditions,    chief    of    which    are 
pregnancy    and    lactation.      Certain    of    the    domestic 
animals  do  not  normally  come  in  heat  while  suckling 
young,  but  to  this  there  are  many  exceptions.    Animals 
having  a  short  period  of  gestation  rarely  or  never  come 
in  heat  while  suckling  young. 

85.  Fertility  and  gestation.  —  Animals  having  a  long 
period  of  gestation  are  less  fertile  than  animals  requiring 
a  shorter  time  for  the  development  of  the  young  in  the 
uterus. 

The  exceptional  fertility  of  the  domestic  sow  is  due 
not  only  to  the  large  number  of  young  born  at  a  time, 
but  to  the  further  fact  that  the  period  of  gestation  is 
only  four  months.  A  sow  may  thus  easily  produce 
two  litters  a  year.  The  mare  produces  but  one  off- 
spring at  a  time,  and  the  period  of  gestation  is  from 
eleven  to  twelve  months.  A  sow,  therefore,  may  give 
birth  to  twenty  young  in  the  same  period  of  time  re- 
quired by  the  mare  for  the  development  and  birth  of 
one  offspring. 

86.  Duration  of  the  reproductive  period.  —  The  fertility 
of  an  individual  or  a  breed  is  largely  determined  by  the 
duration   of   the   reproductive    period.     The   length   of 
this  period  is  a  matter  of  special  importance  in  the  larger 
animals  which  produce  but  one  young  at  a  birth.    The 
breeding  age  is  the  time  from  the  arrival  of  puberty 
until  the  cessation  of  the  breeding  function  on  account 
of  old  age.     The  beginning  of  the  reproductive  period 
has    already    been    discussed     under     puberty.      The 


FERTILITY  89 

average  age  at  which  the  domestic  animals  cease  to 
breed  is  difficult  to  determine  because  of  the  scarcity  of 
records  on  this  point.  The  persistence  of  the  breeding 
powers  of  the  domestic  animal  is  influenced  by  the  condi- 
tions under  which  they  are  reared.  With  favorable 
conditions,  the  mare  has  produced  young  regularly  until 
twenty-five  years  old.  Ewes  have  continued  to  produce 
offspring  until  nineteen  years  of  age. 

87.  Confinement  and  fertility.  —  The  close  confine- 
ment of  animals  seriously  interferes  with  their  fertility. 
Wild  animals  like  the  elephant,  tiger,  lion,  squirrel  and 
monkey  in  captivity  are  often  sterile.  Darwin  states 
that  the  same  animals  breed  more  readily  in  traveling 
shows  than  in  zoological  gardens.  Among  the  domestic 
animals,  confinement  and  lack  of  exercise  are  frequent 
causes  of  a  low  degree  of  fertility.  It  is  generally  a  mis- 
take to  confine  ewes  or  sows  in  a  small  lot  during  the 
winter  months,  under  conditions  which  make  it  impossible 
for  them  to  secure  adequate  exercise.  The  same  may  be 
said  of  males,  including  stallions,  bulls,  boars  and  rams. 
The  comparative  infertility  of  a  stallion  may  often  be 
traced  directly  to  the  fact  that  he  is  kept  stabled  in  a  small 
dark  stall  with  no  regular  exercise.  Mares  both  before 
and  after  breeding  should  be  given  regular  exercise.  It 
is  better  that  they  should  work  at  some  slow  regular  task 
every  day. 

In  an  investigation  on  the  relation  of  exercise  to  the 
development  of  the  internal  organs  by  Kulbs  and  Ber- 
berrich,1  it  was  found  that  in  the  case  of  dogs  and  swine 
the  size  of  the  muscles  and  the  weight  of  the  heart  and 
liver  were  increased  by  exercise.  It  was  also  observed 
that  the  color  of  the  bone  marrow  was  deepened. 

1  "  Jahrbuch  Wiss.  und  Prakt.  Tierzucht,"  6  (1911),  p.  232. 


90  THE   BREEDING   OF  ANIMALS 

Darwin  1  reports  that  "  It  has  been  found  in  France 
that  with  fowls  allowed  considerable  freedom,  only  twenty 
per  cent  of  the  eggs  failed;  when  allowed  less  freedom, 
forty  per  cent  failed ;  and  in  close  confinement,  sixty  out 
of  the  hundred  were  not  hatched." 

88.  The  fertility  of  domesticated  animals.  —  From 
what  has  already  been  said  regarding  confinement  and 
its  deleterious  effect  on  fertility,  it  might  be  concluded 
that  domestication  is  unfavorable  to  high  fertility  in 
animals.  This  is  far  from  the  truth.  Domestication 
furnishes  or  ought  to  furnish  the  most  favorable  conditions 
for  high*  fertility  in  animals.  A  regular  and  abundant 
supply  of  nutritious  food,  shelter  from  a  rigorous  climate, 
and  the  opportunity  for  selection  by  man  all  contribute 
to  the  development  of  a  relatively  high  degree  of  fer- 
tility in  animals.  All  races  of  domestic  animals  are  more 
fertile  than  their  wild  prototypes.  Darwin  has  pointed 
out  that  the  tame  rabbit  gives  birth  to  four  to  eleven  in 
a  litter  and  breeds  six  or  seven  times  a  year,  while  the 
wild  rabbit  only  produces  five  or  six  young  at  one  time 
and  breeds  four  times  yearly.  The  domestic  fowl  may 
produce  as  many  as  200  or  more  eggs  in  one  year,  while 
the  female  of  the  wild  progenitor  of  the  domestic  hen  lays 
only  six  to  ten  eggs  in  a  year.  The  same  remarkable 
difference  exists  between  the  domestic  and  wild  duck. 
The  Indian  Runner  duck  under  domestication  will  pro- 
duce 250  eggs  a  year,  and  the  wild  duck  only  five  to  ten 
eggs  in  one  year.  At  the  Government  Experiment 
Station  of  New  South  Wales  in  Australia,  six  Indian 
Runner  ducks  laid  1601  eggs  in  one  year,  an  average  of 
267  eggs  each. 

1  Darwin,  "Animals  and  Plants  under  Domestication," 
vol.  II. 


FERTILITY  91 

89.  Age   and   fertility.  —  The   fertility   of   animals   is 
influenced  by  age.     Young  animals  that  have  not  yet 
reached  maturity  are  generally  less  fecund  than  mature 
individuals.     There  is  also  some  evidence  to  show  that 
old  mature  animals  are  more  prolific  than  younger  mature 
animals.     It  is  highly  probable  that  skillful  feeding  and 
management  may  result  in  a  significant  increase  as  age 
advances. 

90.  Relation  of  age  to  fertility  in  swine.  —  At  the 
Missouri  Experiment  Station,  the  author  has  had  under 
investigation  the  relation  of  the  age  of  animals  to  their 
breeding  powers.     The  animals  used  in  this  experiment 
have  been  swine,  and  the  general  plan  has  been  to  divide 
the  sows  into  three  groups  according  to  age.     Group  I 
is  composed  of  very  young  sows  from  four  to  five  months 
of  age;    group  II  of  half  mature  sows  about  eighteen 
months  of  age ;  and  group  III  of  mature  sows  from  twenty- 
four  to  thirty  months  old.     The  young  immature  sows 
of  group  I  have  been  bred  at  the  first  appearance  of 
puberty,  which  in  well-fed  sows  is  from  four  to  five  months 
old.     The  female   offspring  of  the   immature   sows  are 
again  bred  at  the  first  appearance  of  he'at,  and  this  will 
be    continued    indefinitely.     A    number    of    interesting 
phenomena  have  been  observed,  but  only  those  results 
which  throw  light  on  the  relation  of  age  to  the  fertility 
of  the  mother  are  recorded  here. 

91.  Influence  of  age  of  sow  on  size  of  litter.  —  In 
the  Missouri   experiment  described   above,   there  have 
been  to  date   (1913)   twenty-six  litters  from  immature 
sows.     The  average  number  of  pigs  to  the  litter  has  been 
four   and    eight-tenths.     From   the   half   mature   sows, 
eight  litters  have  resulted  in  an  average  of  six  and  three- 
tenths  to  a  litter.     The  average  number  of  pigs  in  six 


92  THE   BREEDING   OF   ANIMALS 

litters  from  the  fully  mature  sows  has  been  six  and  five- 
tenths. 

The  sows  used  in  this  experiment  were  all  of  the  same 
breeding,  and  received  the  same  care,  and  the  food,  shelter 
and  all  other  conditions  have  been  similar.  The  differ- 
ences observed  then  must  be  due  to  the  factor  of  age. 
It  will  be  observed  that  there  is  a  marked  difference 
between  the  size  of  the  litters  of  the  immature  sows  and 
the  older  ones.  The  litters  of  the  older  sows  are  materi- 
ally larger  than  from  the  immature  sows. 

The  highest  fertility  in  swine  is  not  reached  until  the 
mother  is  at  or  near  maturity.  It  may  not  always  be 
profitable  for  the  swine-breeder  to  delay  breeding  sows 
until  full  maturity,  but  it  is  apparent  that  when  the  breed- 
ing herd  is  composed  of  older  sows,  a  smaller  number 
need  be  maintained  for  the  production  of  the  pigs  needed 
in  a  given  system  of  farm  management. 

Interesting  statistics  have  been  compiled  by  George 
M.  Rommel 1  from  the  records  of  the  American  Poland- 
China  Record  Association,  which  have  an  important 
bearing  on  this  point.  These  statistics  include  the  breed- 
ing records  of  6145  sows  recorded  in  1902.  There  were 
examined  the  breeding  records  of  2010  one-year  old  sows. 
The  litters  of  1520  one-year-old  sows,  or  seventy-five  per 
cent,  ranged  from  five  to  eight  pigs. 

The  average  litter  of  2047  two-year-old  sows  numbered 
seven  and  five-tenths.  The  number  in  each  litter  of 
1483  sows,  or  seventy-two  per  cent,  ranged  from  six  to 
nine  pigs. 

The  average  number  of  pigs  in  the  litters  of  1157 
three-year-old  sows  was  seven  and  nine-tenths.  The 
average  litter  recorded  for  606  four-year-old  sows  was 

1  American  Breeders'  Association,  Report  19. 


FERTILITY 


93 


eight  and  three-tenths.  The  records  for  325  five-year- 
old  sows  give  the  average  size  of  litter  as  eight  and  seven- 
tenths.  The  total  number  of  sows  examined,  ranging 
in  age  from  one  to  five  years,  was  6145  and  the  average 
size  of  litter  for  the  whole  number  was  seven  and  four- 
tenths. 

The  number  of  animals  included  in  these  investiga- 
tions and  the  unquestioned  accuracy  of  the  records  make 
these  figures  valuable.  It  is  clear  that  the  sows  increase 
in  fertility  from  one  to  five  years.  From  the  standpoint 
of  the  practical  breeder,  it  would  seem  that  sows  from 
two  to  four  years  of  age  will  be  most  profitable  from  the 
standpoint  of  prolificacy. 

92.  Relation  of  age  to  fertility  in  sheep.  —  The  greater 
fertility  of  the  older  females  has  been  noted  in  ewes  by 
the  Wisconsin  Experiment  Station  in  Bulletin  No.  95. 
Observations  made  at  that  station  on  the  percentage  of 
increase  from  ewes  of  different  ages  show  that  two-year- 
old  ewes  gave  an  annual  increase  of  158  per  cent,  three- 

THE   EFFECT  OF   THE  AGE    OF   EWES    ON   PER   CENT   OF   IN- 
CREASE AND  SEX  OF  LAMBS 

WISCONSIN  EXPERIMENT  STATION,  BULLETIN  95 


Two 

THREE 

FOUR 

FIVE 

Six 

SEVEN 

YEARS 

YEARS 

YEARS 

YEARS 

YEARS    . 

YEARS 

AGE  OF  EWE 

BEARING 

No. 

Per 

cent 

No. 

Per 

cent 

No. 

Per 

cent 

No. 

Per 

cent 

No. 

Per 

cent 

No. 

Per 
cent 

Single  Lambs  . 

62 

44.6 

30 

31.9 

21 

80.4 

14 

28.5 

9 

33.3 

6 

60.0 

Pairs  Twins    . 

72 

52.5 

58 

61.7 

42 

60.8 

32 

65.3 

15 

55.5 

3 

30.0 

Sets  Triplets  . 

4 

2.9 

6 

6.4 

6 

8.8 

3 

6.2 

3 

11.2 

1 

10.0 

Rams.     .    .     . 

96 

49.0 

75 

51.0 

71 

57.2 

45 

51.7 

24 

53.3 

10 

66.7 

Ewes  .... 

100 

51.0 

72 

44.0 

S3 

42.8 

42 

48.3 

21 

46.7 

5 

33.3 

-S 

Per  cent 

increase   .    . 

158.0 

174.0 

178.0 

177.0 

178.0 

150.0 

94  THE   BREEDING   OF   ANIMALS 

year-old  ewes  an  increase  of  174  per  cent,  and  four-  to 
six-year-old  ewes  an  increase  of  178  per  cent.  After 
the  age  of  six  years,  there  was  a  distinct  falling  off  in  the 
percentage  of  increase. 

The  foregoing  table  (page  93)  is  reprinted  entire  from 
the  Wisconsin  bulletin  and  is  interesting  as  showing  the 
distribution  of  twin  and  triplet  births  among  the  different 
ages  and  the  sex  of  lambs. 

93.  Influence  of  age  of  ram  on  fertility  of  ewes.  — 
The  number  of  young  at  a  birth  is  generally  believed 
to  be  determined  by  the  number  of  ova  which  are  ripened 
by  the  female  during  any  one  period  of  heat.     The  vigor 
or  age  of  the  male  used  is  not  generally  regarded  as  hav- 
ing any  influence  in  determining  the  number  born  at 
one  time.     The  Wisconsin  Station l  found  that  during 
a  period  of  six  years,  the  flock  of  ewes  served  by  a  year- 
ling ram  produced   150  per  cent  of  lambs.     The  same 
flock  during  a  similar  period  of  six  years  was  served  for 
three    of  these  years  by  two-  and  three-year-old  rams. 
The  average  percentage  of  lambs  born  from  the  older 
rams  was  180  per  cent.     The  author  in  discussing  these 
results   remarks :  "  These  data  are  quite  at  a  variance 
with  the  opinion  commonly  held  by  sheepmen,  generally 
to  the  effect  that  a  well  grown,  vigorous  yearling  ram 
is  at  his  best  as  a  sire.     It  is  also  contrary  to  the  belief 
held  by  many  that  the  vigor  of  the  sire  has  no  apparent 
influence  on  the  percentage  of  increase." 

94.  The  effect  of  the  age  of  poultry  parents  on  the 
offspring.  —  The   general   conclusion  that   fully  mature 
animals  are  more  fertile  seems  to  be  substantiated  by 
the  poultry-breeding  experiment  conducted  by  Atwood.2 

1  Wisconsin  Experiment  Station,  Bulletin  95. 

2  Atwood,  West  Virginia  Experiment  Station,  Bulletin  No.  124. 


FERTILITY 


95 


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96  THE   BREEDING  OF   ANIMALS 

In  this  investigation,  Single  Comb  White  Leghorns  were 
employed  and  a  comparison  of  hens,  pullets,  two-year 
and  three-year-old  hens  was  made.  The  important  results 
may  be  seen  at  a  glance  from  the  table  (page  95). 

The  records  of  this  test  show  that  the  eggs  laid  by  old 
hens  are  heavier  than  those  laid  by  pullets,  that  the  num- 
ber of  chicks  hatched  was  ten  per  cent  greater,  that  the 
initial  weight  at  hatching  time,  and  for  several  weeks 
thereafter,  was  greater  from  the  older  hens,  and  finally 
that  the  percentage  of  chicks  dying  from  pullet's  eggs 
was  three  times  greater  than  from  the  mature  hens. 

In  marked  contrast  to  the  above  results  are  those 
published  by  the  Maine  Experiment  Station  in  Bulletin 
168.  The  author  (Pearl)  of  this  publication  states, 
"  The  present  statistics  do  not  show  any  marked  superi- 
ority of  hens  over  pullets  in  respect  to  breeding  perform- 
ance, so  far  as  either  fertility  or  hatching  quality  of  eggs 
are  concerned." 

95.  Age  and  fecundity.  —  Duncan x  distinguishes  be- 
tween the  ability  to  bear  children,  which  he  calls  fecundity, 
from  actual  productiveness  or  the  number  of  births,  which 
is  designated  as  fertility.  From  Duncan's  investigations 
it  is  possible  to  formulate  a  general  law  which  represents 
a  true  statement  of  the  relation  of  age  to  fecundity.  This 
general  law  has  been  stated  by  Marshall  2  as  follows : 
"  The  fecundity  of  the  average  individual  woman  may  be 
described,  therefore,  as  forming  a  wave,  which,  starting 
from  sterility,  rises  somewhat  rapidly  to  its  highest  point 
and  then  gradually  falls  again  to  sterility."  The  results 
discussed  earlier  in  this  chapter  clearly  indicate  that  in 

1  Duncan,  "Fecundity,  Fertility,  Sterility  and  Allied  Topics," 
Edinburgh,  1866. 

2  Marshall,  "The  Physiology  of  Reproduction,"  p.  590. 


FERTILITY  97 

the  case  of  swine  this  law  is  undoubtedly  a  true  statement 
of  what  actually  happens.  This  law  not  only  applies 
to  mammals  but  is  also  found  in  poultry.  Geyelin 1  has 
attempted  to  formulate  an  average  of  fertility  in  poultry 
in  relation  to  age  in  the  following  table : 


First  Year  after  hatching  . 
Second  Year  after  hatching 
Third  Year  after  hatching  . 
Fourth  Year  after  hatching 
Fifth  Year  after  hatching  . 
Sixth  Year  after  hatching  . 
Seventh  Year  after  hatching 
Eighth  Year  after  hatching 
Ninth  Year  after  hatching  . 


15  to    20  eggs 

100  to  120  eggs 

120  to  135  eggs 

100  to  115  eggs 

60  to    80  eggs 

50  to    60  eggs 

35  to    40  eggs 

15  to    20  eggs 

1  to    10  eggs 


These  estimates  must  be  regarded  as  far  below  the 
performance  of  well-selected  flocks  maintained  under 
good  conditions  of  food  and  shelter.  The  age  at  which 
pullets  begin  laying  varies  greatly,  depending  upon  their 
development.  At  the  Ohio  Experiment  Station,  a  White 
Leghorn  pullet  began  laying  at  four  months  and  fifteen 
days  old.  At  the  Missouri  Experiment  Station  Kempster 2 
reports  a  White  Leghorn  pullet  beginning  to  lay  at  four 
months  and  nineteen  days  of  age.  The  number  of  eggs 
laid  by  old  hens  may  also  greatly  exceed  the  figures  given 
by  Geyelin.  At  the  Maine  Experiment  Station  a  hen 
laid  111  eggs  during  her  ninth  year.3 

A  remarkable  case  of  fecundity  in  sheep  is  noted  by 
Pearl.4  A  ewe  owned  by  Barrett  for  nineteen  years 
gave  birth  to  thirty-six  lambs  which  were  distributed 
during  the  breeding  life  of  the  ewe  as  follows  (page  98) : 

1  Geyelin,  quoted  by  Marshall,  loc.  cit.,  p.  590. 

2  Unpublished  records,  Missouri  Experiment  Station. 

3  Maine  Experiment  Station,  Bulletin  266. 

4  Pearl,  Science,  vol.  37,  p.  227. 


98  THE   BREEDING  OF   ANIMALS 

LAMBS 

April,  1806 .  1 

1807 1 

1808 2 

Aprils,  1809 3 

March  29,  1810 3 

Making  6  lambs  in  11  months  and  26  days 

1811 3 

1812 3 

1813 .3 

1814 .3 

1815 2 

1816 2 

1817 2 

1818 2 

1819 2 

1820 2 

1821 1 

1822 1 

1823 0 

1824 _0 

Total 36 

Pearl  has  further  called  attention  to  the  fact  that 
"  the  median  point  in  the  breeding  career  of  this  ewe  was 
8.17  years.  That  is,  she  produced  one-half  of  her  offspring 
before  and  one-half  after  it."  The  age  of  maximum  fe- 
cundity in  this  ewe  was  7.34  years. 

96.  Nutrition  and  fertility.  —  All  the  physiological 
activities  of  an  animal  are  influenced  by  nutrition.  This 
is  particularly  the  case  with  the  reproductive  functions. 
The  fertility  of  an  animal  is  influenced  by  the  kind  and 
the  amount  of  food  consumed.  Certain  kinds  of  food 
have  long  been  believed  to  affect  injuriously  the  breeding 
functions  of  animals.  Sugar  fed  to  domestic  animals 
in  considerable  amounts  has  apparently  had  an  unfavor- 
able influence  on  fertility.1  Greatly  increased  activity 

1  Tanner,  Journal  of  Royal  Agricultural  Society,  1865,  p.  267. 


FERTILITY  99 

of  the  generative  organs  is  characteristic  of  the  spring 
season.  At  this  season  most  animals,  domestic  and  wild, 
are  periodically  in  heat.  This  greater  activity  is  un- 
doubtedly due  to  the  abundant  supply  of  nutritious  and 
succulent  grass.  That  this  kind  of  food  does  materially 
influence  the  fertility  of  animals  is  recognized  by  the 
shepherds  of  England  in  the  practice  of  flushing  ewes. 
This  practice  consists  in  turning  the  ewe  flock  on  rich 
succulent  pastures  about  two  weeks  before  turning  in 
the  ram.  The  flock  owners  believe  that  this  increases 
the  number  of  lambs  and  brings  the  ewes  more  uniformly 
in  heat.  The  Beinn  Bhreagh  x  flock  of  sheep  in  Nova 
Scotia  belonging  to  Dr.  Bell  when  fed  generously  before 
and  during  the  mating  season  produced  a  larger  number 
of  twins.  The  older  ewes  also  produced  a  larger  per- 
centage of  twins. 

97.  Excessive  food  supply  and  nutrition.  —  An  over- 
supply  of  nutritious  food  which  causes  the  animal  to 
become  abnormally  fat  is  often  the  cause  of  sterility 
among  the  domestic  animals.  In  nature  it  is  rare  for 
an  animal  to  remain  continuously  in  an  excessively  fat 
condition.  At  certain  seasons  of  abundant  food  supply 
the  wild  animal  may  become  fat,  but  such  periods  of 
plethora  are  invariably  followed  by  a  scarcity  of  food, 
and  such  food  must  often  be  gathered  by  exhaustive 
exercise.  Such  variations,  if  not  extreme,  may  be  partic- 
ularly favorable  for  the  functioning  of  the  reproductive 
system.  Certain  it  is  that  the  most  skillful  stockmen 
have  long  recognized  the  fact  that  the  female  reproduc- 
tive functions  are  most  active  when  the  individual  is 
actually  gaining  in  condition.  An  animal  that  is  main- 
tained in  a  uniform  condition  of  excessive  fatness  is  not 

1  Bell,  Journal  of  Heredity,  vol.  V,  p.  47. 


100  THE   BREEDING   OF   ANIMALS 

in  the  best  condition  for  the  successful  exercise  of  the 
breeding  function.  A  rapidly  improving  condition  due 
to  nutritious  food  supplied  in  generous  quantities  is 
distinctly  favorable,  provided  the  animal  is  not  already 
too  fat. 

E.  Davenport  has  held  that,  "  excessive  food  supply 
leads  to  infertility  among  both  plants  and  animals." 
This  is  true  of  long-continued  and  excessive  feeding,  but 
a  rapidly  improving  condition  of  the  animal  in  thin  condi- 
tion is  distinctly  favorable  to  the  highest  fertility.  It  is 
a  mistaken  idea  that  starvation  or  a  very  limited  diet 
is  a  favorable  environment  for  the  successful  activity  of 
the  generative  system.  Such  treatment  is  only  favorable 
in  the  case  of  over-fat  animals  and  is  oftener  the  first 
and  a  very  essential  step  in  securing  offspring  from  animals 
that  through  a  long  period  of  overfeeding  become  tem- 
porarily barren. 

98.  Other  factors  affecting  fertility.  —  A  sudden  change 
of  conditions  surrounding  the  animal,  such  for  example 
as  the  exportation  of  an  animal  from  Europe  to  the  United 
States,  will  often  temporarily  interfere  with  the  normal 
activities  of  the  reproductive  system  and  the  animal 
may  be  barren  for  a  time.  When  the  animal  has  become 
thoroughly  accustomed  to  the  changed  conditions,  its 
breeding  powers  return  and  thereafter  may  function 
normally.  Changed  conditions  may  also  result  in  in- 
creased fertility.  As  shown  elsewhere,  breeding  animals 
in  thin  condition  and  existing  upon  a  sparse  ration  or  upon 
a  dry  dietary,  become  markedly  more  fertile  when  changed 
to  richer  pastures. 

Some  individuals  are  infertile  when  mated  with  cer- 
tain other  individuals,  but  may  be  fully  fertile  with  others. 
A  mare  may  be  sterile  when  bred  to  a  stallion,  but  fertile 


^;/O£i'j-  ;Aioi 

when  mated  with  a  jack.  Such  a  physiological  aversion 
is  not  easy  to  explain,  but  is  nevertheless  so  frequent  as 
to  be  a  well-recognized  fact  among  breeders.  Prolonged 
lactation  must  be  regarded  as  unfavorable  to  fecundity 
in  some  species.  This  is  especially  true  in  the  case  of 
swine,  where  early  weaning  of  the  litter  will  certainly 
encourage  an  earlier  return  of  the  heat  period  and  thus 
make  possible  a  larger  number  of  litters  during  the  natural 
breeding  life  of  the  mother. 

99.  Relation  of  number  of  mammae  in  swine  to  fertility. 
—  An  interesting  study  of    the   mammae  in  swine  was 
reported  by  Wentworth.1     From  these  researches  there 
is  little  evidence  in  favor  of  the  popularly  accepted  opinion 
that  there  is  a  relation  between  the  fertility  of  swine  and 
the  number  of  mammae.     The  normal  type  of  mammary 
pattern  in  swine  consists  of  regularly  placed  pairs  on  the 
ventral  side  of  the  body.     The  first  pair  lie  immediately 
behind   the   juncture    of   the    ribs    and    sternum.    The 
greatest  variation  occurs  in  the  second  pair.    The  last 
pair  are  closer  together  and  thus  nearer  the  median  line 
in  an  inguinal  position.     Variations  occur  in  the  number 
of  pairs  and  also  in  the  suppression  of  one  nipple  of  a 
pair.     These  variations  are  often  inherited.     The  normal 
number  of  mammae  in  the    Tamworth    and   Berkshire 
breeds  is  13,  14  and  15,  in  the  Duroc-Jersey  breed  10, 
11  and  12.     The  tendency  to  vary  is  greater  when  the 
number  of  pairs  exceeds  five. 

100.  Twins.  —  The  normal  number  of  young  in  several 
of  the  larger  breeds  of  the  domestic  animals  and  in  man 
is  one.    The  production  of  a  larger  number  at  a  single 
birth  is  exceptional.     It  happens,  however,  that  twins 
are  frequently  born,  while  triplets  and  even  four  and 

1  Wentworth,  Amer.  Naturalist,  vol.  47,  p.  257. 


102  ^\}:f0$$^£E&I$G  OF  ANIMALS 

five  at  a  birth  have  been  reported.  When  twins  are 
born  they  are  either  of  identical  sex  or  one  a  male  and 
the  other  a  female.  In  some  cases  the  twins  are  very 
much  alike  in  all  other  characters  as  well  as  sex.  Such 
twins  were  called  by  Galton  identical  twins.  It  is  also 
true  that  twins  are  often  born  which  have  no  greater 
resemblance  to  one  another  than  ordinary  brothers  and 
sisters.  Such  twins  undoubtedly  develop  from  separate 
eggs  and  are  known  as  ordinary  or  fraternal  twins.  They 
do  not  necessarily  resemble  one  another  more  closely 
than  brothers  and  sisters  of  the  same  family  except 
that  they  are  of  identical  age  and  for  this  reason  might 
be  expected  to  have  a  closer  resemblance  than  brothers 
or  sisters  of  widely  different  ages.  Fraternal  twins  may 
be  of  different  sex.  Identical  twins  are  believed  to  come 
from  one  egg  after  fertilization.  They  are  always  of  the 
same  sex  and  very  much  alike  in  external  and  internal 
character  and  in  mental  and  moral  tendencies. 

101.  Characters  correlated  with  fertility.  —  It  is  in  the 
highest  degree  desirable  that  the  breeder  should  be  able 
to  distinguish  those  qualities,  external  and  internal, 
which  are  in  any  way  correlated  either  with  fertility  or 
sterility.  Unfortunately  we  cannot  now  speak  with  as- 
surance on  all  the  supposed  evidences  of  fertility  in 
animals,  but  some  characters  are  undoubtedly  closely 
correlated  with  fertility  and  we  may  through  them  learn 
to  judge  of  the  probable  existence  or  nonexistence  of 
this  most  desirable  trait.  Manifestly,  characters  closely 
correlated  with  fertility  will  finally  persist  and  become 
dominant.  It  is  equally  evident  that  those  characters 
of  the  animal  body  which  are  correlated  with  infertility 
will  ultimately  disappear.  The  skillful  judge  of  breed- 
ing animals  recognizes  some  such  correlation  in  the  selec- 


FERTILITY  103 

tion  of  both  male  and  female  individuals.  The  breeder 
emphasizes  the  existence  of  those  general  qualities  which 
give  to  the  male  a  distinctly  masculine  appearance  and 
to  the  female  a  clearly  recognizable  character  of  femininity. 
The  bull  possessing  a  markedly  masculine  aspect  is  held 
to  be  a  "  good  breeder."  Whether  it  is  meant  by  this 
that  such  a  bull  is  prepotent  in  fixing  his  own  charac- 
teristics upon  his  offspring  or,  what  is  more  probable, 
that  a  bull  of  this  character  is  more  than  ordinarily  effi- 
cient in  the  development  of  sperm-cells,  it  is  still  true 
that  the  masculine  type  may  be  regarded  as  in  some 
degree  at  least  correlated  with  fertility.  Supernumerary 
mammae  have  been  found  in  many  cases  associated  with 
exceptional  fertility.  In  describing  the  dam  of  triplet 
calves,  Pearl 1  remarks :  "  It  is  of  interest  to  note  that 
this  cow  has  two  very  small  posterior  mammae.  It  is 
of  course  impossible  to  say  whether  this  occurrence  of 
supernumerary  mammae  is  directly  connected  with  the 
high  degree  of  fecundity  exhibited  by  this  cow,  but  this 
may  fairly  be  regarded  as  probably  the  case  because  of 
the  fact  that  these  two  things  are  known  to  be  associated 
in  other  forms."  The  sheep  breeding  experiments  at 
Beinn  Bhreagh2  by  Alexander  Graham  Bell  have  suggested 
a  possible  correlation  between  extra  nipples  and  unusual 
fecundity.  Stature  and  fertility  have  been  found  by 
Pearson  3  to  be  somewhat  closely  correlated  among  women. 
The  taller  women  are  on  the  average  more  fertile.  If  this 
is  generally  true,  the  stature  of  women  is  likely  to  increase 
at  least  until  it  has  reached  a  point  which  satisfies  the 
correlation  existing.  Among  swine-breeders  it  is  generally 

1  Loc.  tit. 

2  Bell,  Science,  N.  S.,  vol.  36,  pp.  378-384. 

3  Pearson,  "Grammar  of  Science,"  pp.  441-445. 


104  THE   BREEDING  OF  ANIMALS 

believed  that  sows  with  rather  long  bodies  are  more  fertile 
than  shorter,  more  compact  individuals.  It  seems  to  be 
true  also  that  females  having  a  somewhat  loose  and  open 
conformation  are  generally  more  certain  breeders. 

The  milking  function  of  animals  is  in  a  measure  corre- 
lated with  the  quality  of  fecundity.  Breeds  of  animals 
and  individuals  which  have  the  milking  function  well 
developed  are  more  fecund  than  those  in  which  the  devel- 
opment of  this  quality  has  been  neglected.  Tanner,1 
in  his  interesting  discussion  on  "  The  Reproductive 
Powers  of  Animals,"  says :  "  The  formation  of  milk  is 
intimately  correlated  with  the  reproductive  powers. 
The  secretion  of  milk  is  dependent  upon  the  activity  of 
the  mammary  glands  and  these  are  either  under  the  direct 
influence  of  the  breeding  organs  or  else  they  sympathize 
very  closely  with  them.  Those  animals  which  breed 
with  the  least  difficulty  yield  the  best  supplies  of  milk 
and  produce  the  most  healthy  and  vigorous  offspring." 
He  also  adds  that,  "  Since  a  short  supply  of  milk  is  indica- 
tive of  and  associated  with  enfeebled  breeding  powers 
every  care  should  be  taken  to  obviate  this  defect." 

It  must  be  admitted  that  our  knowledge  on  the  sub- 
ject of  characters  correlated  with  fertility  is  as  yet  frag- 
mentary and  indefinite.  The  importance  of  this  quality 
in  practical  breeding  should  make  this  a  fruitful  field 
for  further  investigation. 

102.  In-breeding  and  fertility.  —  Continuous  in-breed- 
ing among  domestic  animals  has  in  many  instances  been 
followed  by  low  fecundity  or  absolute  sterility.  It  is 
generally  believed  by  practical  breeders  that  of  all  the 
ill  effects  supposed  to  result  from  in-breeding,  lessened 

1  Tanner,  "The  Reproductive  Powers  of  Animals,"  Journal 
of  Royal  Agricultural  Society,  1865,  p.  270. 


FERTILITY  105 

fertility  is  the  one  most  likely  to  follow.  Whether  this 
loss  of  fecundity  in  animals  of  consanguineous  breeding 
is  to  be  attributed  to  in-breeding  per  se  or  whether  it  is 
due  to  the  rapid  fixing  of  a  tendency  to  sterility  already 
existing  in  the  family,  it  is  nevertheless  true  that  there 
exists  a  certain  amount  of  probability  that  continuous 
close-breeding  will  ultimately  affect  injuriously  the 
fertility  of  animals.  This  question  is  discussed  at  some 
length  under  "  In-breeding,"  Chapter  XI. 

103.  Cross-breeding  and  fertility.  —  It  naturally  fol- 
lows that  if  in-breeding  is  unfavorable  to  full  fecundity, 
cross-breeding  must  tend  to  develop  this  desirable  quality. 
Here  again  it  is  not  easy  to  trace  the  increased  fertility 
which  follows  the  mating  of  animals  of  diverse  characters 
to  the  sole  act  of  crossing.  Many  of  the  cases  of  increased 
fecundity  due  to  crossing  may  be  explained  on  the  basis 
of  introducing  the  new  quality  of  high  fertility.  If  fertil- 
ity is  a  dominant  character  transmitted  in  accordance 
with  the  Mendelian  principle  of  dominance,  it  is  easy  to 
understand  why  the  cross-bred  animal  may  exhibit,  as 
it  often  does,  a  greater  degree  of  fecundity  than  can  be 
accounted  for  on  the  assumption  of  blended  inheritance 
of  this  quality  from  both  parents.  What  actually  happens 
is  that  one  of  the  parents  possesses  the  quality  of  fertility 
in  high  degree  and  this  becomes  dominant  in  the  offspring. 
A  certain  proportion  of  the  offspring,  therefore,  receive 
in  the  constitution  of  the  germ-plasm  all  the  high  fertility 
which  is  an  inherent  part  of  the  germ  substance  of  the  one 
parent.  It  should  also  follow  that  a  certain  proportion  of 
the  offspring  inherit  unchanged  the  tendency  to  low  fecun- 
dity characteristic  of  the  other  parent.  It  must  be  ad- 
mitted that  evidences  of  the  latter  are  still  lacking,  but  it 
should  be  possible  by  experiment  to  determine  this  point. 


106  THE   BREEDING   OF   ANIMALS 

104.  Unusual  fertility.  —  Each  species  and  most  varie- 
ties or  breeds  of  animals  have  a  fairly  uniform  and  normal 
rate  of  increase.    Thus  the  normal  number  of  young  at  a 
birth  in  cattle  and  horses  is  one.     It  is  also  probably 
true  that  among  sheep  one  is  the  normal  number  of  young 
at  each  birth.     But  many  breeds  of  sheep  have  been 
so  changed  by  domestication  that  twins  are  frequent 
and  triplets  are  not  rare.     The  quality  of  fertility  is 
undoubtedly  transmitted  by  heredity.     It  is  therefore 
possible  to  increase  the  normal  fertility  of  the  domestic 
sheep   by   selection.     Among   cattle   the   production   of 
twins  has  not  been  regarded  as  a  particularly  desirable 
quality,  and  hence  no  attempt  has  been  made  to  increase 
the  normal  birth  number  of  the  bovine  species.     It  is 
not  difficult,  however,  to  conceive  that  it  would  be  com- 
paratively easy  to  develop  a  breed  or  variety  of  cattle 
which  would  produce  twins.     Cases  of  unusual  fertility 
among  all  classes  of  the  domestic  animals  are  frequent. 
These  are  of  enough  importance  from  a  practical  point 
of  view  and  of  sufficient  biological  significance  to  be  given 
a  place  in  a  discussion  on  fertility. 

105.  Unusual   fertility   among   horses.  —  Exceptional 
fertility  among  horses  is  generally  to  be  found  in  connec- 
tion with  longevity  and  active  and  regular  functioning 
of  the  breeding  powers  rather  than  in  unusual  numbers 
of  young  at  a  birth.     A  mare  twenty-five  years  old,  owned 
by  R.  O'Heren  of  Illinois,  in  1904  was  suckling  her  twen- 
tieth colt.     She  was  one-half  Thoroughbred  and  one-half 
Clydesdale  and  was  still  strong  and  active.1    The  Thor- 
oughbred mare,  Fanny  Cook,  dam  of  Daniel  Lambert, 
produced  fifteen  foals  and  dropped  twins  at  twenty-two 

1  Reported  in  a  letter  to  the  author  by  R.  H.  Dunn,  Illiopolis, 
111. 


FERTILITY  107 

years  of  age.  A  Clydesdale  mare  belonging  to  G.  W. 
Henry  of  Burlington,  Iowa,  was  the  mother  of  nine- 
teen foals  and  was  supposed  to  be  in  foal  again.1  Poca- 
hontas,  a  running  mare,  was  the  mother  of  fifteen  foals 
and  dropped  her  last  at  the  time  she  was  twenty-five 
years  of  age. 

106.  Unusual  fertility  among  cattle.  —  Some  remark- 
able cases  of  fecundity  among  cattle  have  been  recorded. 
In  most  cases  the  ability  to  ripen  a  number  of  eggs  dur- 
ing one  period  of  heat  seems  to  be  inherent.  A  cow  that 
has  produced  twins  or  triplets  is  very  apt  to  do  so  again. 
This  tendency  to  multiple  gestation  in  cattle  is  well 
illustrated  by  a  family  of  cattle  on  a  New  Hampshire 
farm  reported  by  Wentworth.2  "  The  foundress  of  the 
family  was  a  grade  Holstein  cow,  herself  a  twin,  about 
seven  years  old.  She  has  been  on  the  farm  ever  since 
she  was  dropped  and  has  given  birth  to  seven  calves. 
Her  first  service  was  to  a  Guernsey  bull  and  resulted  in  a 
pair  of  yellow  and  white  heifers,  one  of  which  is  now  in 
the  herd.  Her  second  mating  to  a  red  Shorthorn  bull 
resulted  in  a  single  black  and  white  bull  calf  that  was 
vealed.  An  Ayrshire  bull  sired  her  third  calves,  twin 
black  and  white  bulls,  but  neither  of  these  was  good 
enough  to  raise.  Her  fourth  service  was  to  a  Holstein 
bull  and  from  it  she  produced  twin  black  and  white  heifers 
that  promise  well  as  milkers." 

"  The  yellow  and  white  twin  first  produced  by  the 
old  cow  is  now  four  years  old  and  has  twice  borne  twins. 
To  an  Ayrshire  bull  she  produced  a  pair  of  yellow  and 
white  bull  calves  that  early  went  to  the  butcher  and  to  a 

1  Sanders,  "Horse  Breeding,"  p.  179. 

2  Wentworth,  E.  N.,  "  Twins  in  Three  Generations,"  Breeder's 
Gazette,  vol.  62,  p.  133. 


108  THE   BREEDING  OF  ANIMALS 

Holstein  bull  she  gave  birth  to  twin  black  and  white 
heifers  last  December." 

Pearl 1  has  described  an  interesting  case  of  triplet 
calves  from  a  grade  Guernsey  cow  seven  years  old.  The 
sire  was  a  young  grade  Hereford  bull  which  had  not 
shown  any  unusual  tendency  to  sire  twins  or  triplets. 
Two  of  the  calves  were  heifers  and  had  the  typical  white 
face  of  the  Hereford  breed.  The  third  calf,  a  bull,  was 
a  typical  Guernsey  and  in  color  and  coat  markings  re- 
sembled somewhat  closely  his  dam.  (Plate  IV.) 

In  reference  to  the  breeding  record  of  these  triplet 
calves,  Pearl  says:  "The  writer  asked  Mr.  Walter, 
the  owner  of  the  calves  here  described,  to  pay  particular 
attention  to  the  sexual  behavior  of  these  triplets.  This 
was  done.  As  has  already  been  implied  in  what  has  gone 
before,  the  male  individual  of  the  triplets  was  entirely 
functional  sexually.  He  was  used  in  service  locally; 
got  good  calves ;  and  apparently  got  as  high  a  proportion 
of  calves  as  would  be  expected  from  a  bull  of  his  age.  In 
regard  to  the  sexual  history  of  the  female  individuals 
of  the  triplets,  Mr.  Walter  has  the  following  to  say  in  a 
letter  dated  April  11,  1910.  After  noting  the  fact  that 
these  two  supposed  heifers  had  been  killed  and  sold  in 
the  village  market  he  says :  '  Neither  of  them  had 
ever  been  in  heat/  In  earlier  letters  Mr.  Walter  on  sev- 
eral occasions  said  that  these  calves  never  showed  the 
slightest  signs  of  being  in  heat.  From  the  account  given 
by  the  butcher  who  killed  these  animals  it  appears  prob- 
able that  in  both  individuals  the  conditions  were  such  as 
have  been  described  for  many  free-martins.  Neither 
uterus  or  tubes  were  recognized,  but  the  vagina  apparently 

1  Pearl,  "Triplet  Calves,"  Bulletin  204,  Maine  Agricultural 
Experiment  Station. 


PLATE  IV.  —  Unusual  fertility  in  the  cow.     Triplet  calves  from  a 
grade  Guernsey  dam  and  grade  Hereford  sire. 


FERTILITY  109 

ended  at  its  anterior  end  as  a  blind  sack.  Although 
detailed  anatomical  data  are  lacking,  there  can  be 
little  doubt,  I  believe,  because  of  both  physiological 
fact  and  absence  of  restrus  and  the  lack  (?)  or  minute, 
infantile  condition  of  uterus  and  Fallopian  tubes,  that 
these  two  supposed  female  individuals  were  really  free- 
martins." 

The  cow  possessed  two  supernumerary  mammae  just 
behind  the  posterior  pair.  The  occurrence  of  super- 
numerary mammae  has  before  been  observed  to  accom- 
pany the  tendency  to  multiple  births. 

A  seven-year-old  Shorthorn  cow  dropped  seven  dead 
calves  at  one  birth.  They  were  sired  by  a  Holstein  bull.1 
A  Shorthorn  cow  three  years  old,  on  post  mortem,  was 
found  to  be  carrying  six  perfectly  developed  calves  in 
her  uterus.2  Another  Shorthorn  cow  gave  birth  to  four 
calves,  three  of  which  were  weak  and  undeveloped.3  A 
cross-bred  cow  gave  birth  to  seven  calves  within  a  period 
of  twelve  months.  All  these  calves  were  born  alive.4 
A  cow  dropped  three  pairs  of  twins  in  succession  during 
a  period  of  two  years.5  A  grade  Guernsey  cow  on  a  farm 
in  Washington  County,  Pennsylvania,  gave  birth  to 
triplets.  This  cow  was  ten  years  old  and  had  produced 
fifteen  calves  at  eight  births.  A  cow  twenty-two  years 
old  ^is  reported  as  having  had  twenty  calves  and  was 
again  pregnant.6  A  remarkable  case  of  continued  high 
fertility  in  a  cow  is  quoted  by  Pearl  from  McGillwray's 
"  Manual  of  Veterinary  Science  and  Practice."  The  cow 

1  Country  Gentleman,  1895,  p.  595. 

2  Ibid.,  1880,  p.  313. 

3  Ibid.,  1891,  p.  339. 

4  Ibid.,  1893,  p.  231. 

5  Breeder's  Gazette,  1898,  p.  7. 

6  Rural  New-Yorker,  1906,  December. 


110  THE   BREEDING   OF   ANIMALS 

described   was   of   "  the   black  polled   breed  "   and   her 
record  of  births  follows : 

YEAR    NUMBER  OP  CALVES  AT  BIRTH 

1842    .  1         This  the  cow's  first  calf 


1843 
1843 
1844 
1845 
1846 
1847 
1848 


3  All  lived  to  adult  age 

4  One  died.     (Seven  calves  in  one  year) 

2  Lived  to  maturity 

3  Lived  to  maturity 

6  All  died  prematurely 

2  Came  to  maturity 
4 


Total.     .     .     25      Mean  number  per  birth — '3.125 

107.  Unusual  fertility  among  sheep.  —  Sheep  normally 
produce  a  larger  proportion  of  twins  than  cattle  or  horses. 
This  may  be  due  in  a  measure  to  the  fact  that  the  sheep 
has  a  much  shorter  period  of  gestation.  It  is  true  in 
general  that  those  mammals  having  the  shortest  periods 
of  gestation  are  most  prolific.  Some  remarkable  cases 
of  great  fertility  among  sheep  are  matters  of  record. 
A  three-year-old  grade  Cotswold  ewe  gave  birth  to  five 
fully  developed  lambs.  Two  died  at  birth,  the  others  in 
a  few  hours.1  A  Horned  Dorset  ewe  four  years  old 
dropped  five  lambs  at  two  births  within  a  ten  months' 
period.2  A  Radnor  ewe  dropped  six  lambs  at  one  birth, 
of  which  five  lived  and  thrived.3  An  Oxford-down  ewe 
gave  birth  to  four  strong,  vigorous  lambs  which  grew 
rapidly  and  weighed  one  hundred  and  sixty-two  pounds 
at  eight  weeks  old.4  A  prolific  ewe  at  one  birth  dropped 
five  lambs,  all  of  which  were  perfectly  developed  and  grew 
rapidly.5  A  Leicester  ewe  gave  birth  to  six  strong,  healthy 

1  Country  Gentleman,  1893,  p.  171. 

2  Breeder's  Gazette,  1894,  p.  327. 

3  Country  Gentleman,  1892,  p.  331. 

4  Breeder's  Gazette,  1893,  p.  388. 

5  Country  Gentleman,  1878,  p.  329. 


FERTILITY  111 

lambs,  four  of  which  the  mother  nursed  successfully. 
The  earless  Shanghai  breed  of  sheep  exhibited  in  the 
London  Zoological  Gardens  in  1857  seem  to  have  inherited 
a  remarkable  fecundity.  Bartlett 1  has  described  this 
variety  as  breeding  twice  each  year  and  often  producing 
four  or  five  at  a  birth.  In  the  spring  of  1857  three  ewes 
of  this  breed  gave  birth  to  thirteen  lambs. 

108.  Unusual  fertility  among  swine.  —  There  is  more 
difficulty  in  determining  the  normal  number  of  young  at 
a  birth  among  swine  than  among  other  domestic  animals. 
There  is  considerable  variation  among  individuals  belong- 
ing to  the  same  breed  and  between  different  breeds. 
Some  particular  cases  of  high  fertility  are  described 
below : 

A  three-year-old  Chester  White  sow  2  farrowed  ninety- 
six  pigs  in  six  litters.  There  were  fourteen  in  each  of 
the  first  three  litters  and  eighteen  in  each  of  those  last 
farrowed.  This  tendency  among  highly  fecund  indi- 
viduals to  give  birth  to  larger  and  larger  numbers  has 
been  observed  in  cattle,  sheep  and  swine. 

A  Poland  China  sow 3  produced  thirty-four  living  pigs 
in  three  litters  during  a  single  twelve  months'  period. 

A  sow  4  gave  birth  to  twenty-one  pigs  in  a  litter.  Pre- 
vious to  this  she  had  farrowed  two  litters  of  fifteen  and 
seventeen  pigs  each.  A  sow  of  uncertain  breed  5  dropped 
twenty-three  pigs  in  one  litter.  All  but  two  of  these 
were  born  alive.  The  same  sow  gave  birth  to  eighty- 
five  pigs  in  five  litters.  Ray  L.  Zimmerman  of  Amazonia, 
Andrew  County,  Missouri,  reports  to  the  author  that  a 

1  Bartlett,  Proc.  Zool.  Soc.,  London,  1857,  p.  105. 

2  Breeder's  Gazette,  1897,  p.  368. 

3  Ibid.,  1894,  p.  308. 

4  Country  Gentleman,  1887,  p.  281. 
6  Ibid.,  1894,  p.  915. 


112  THE   BREEDING  OF  ANIMALS 

Poland  China  sow  owned  by  W.  Minner  of  that  county 
farrowed  twenty-five  pigs  in  one  litter. 

109.  Unusual  fertility  among  poultry.  —  An  instance 
of  remarkable  ability  in  egg-laying  is  given  in  the  Experi- 
ment Station  Record,  vol.  28,  p.  270.  In  this  volume  is 
described  a  Single  Comb  Brown  Leghorn  hen  which  laid 
257  eggs  in  twelve  months.  This  hen  weighed  only 
three  and  two-tenths  pounds.  The  average  weight  of 
the  eggs  was  one  and  eight-tenths  ounces.  At  the  Dela- 
ware Experiment  Station  a  White  Leghorn  hen,  Lady 
Eglantine,  laid  314  eggs  in  one  year. 


CHAPTER  VI 
STERILITY 

IT  goes  without  saying  that  the  first  essential  quality 
in  a  breeding  animal  is  the  ability  to  produce  young. 
The  more  highly  developed  the  animal  is  in  those  special 
characters  which  have  been  fixed  by  selection,  the  more 
important  becomes  the  mere  ability  of  an  individual  to 
give  birth  to  offspring.  In  an  animal  reared  primarily 
for  commercial  purposes,  like  the  hog  or  the  beef  type, 
the  barren  individual  is  not  so  serious  a  loss,  as  it  may 
still  have  a  value  for  meat. 

It  is  well  known  that  many  individuals  among  the 
domestic  animals  are  sterile.  Such  sterility  is  found 
among  animals  reared  under  the  best  conditions,  as  well 
as  among  those  subjected  to  less  skillful  husbandry. 
Barrenness  occurs  in  individuals  which  are  a  part  of 
herds  or  flocks  in  which  all  animals  are  surrounded  by 
identically  the  same  conditions.  It  must  be  true,  there- 
fore, that  some  animals  possess  a  tendency  to  barrenness 
in  a  more  marked  degree  than  others.  This  tendency 
may  possibly  be  inherited.  Barrenness  may  be  only 
temporary  or  it  may  be  a  permanent  condition.  When  it 
is  a  temporary  condition,  it  can  often  be  alleviated  by 
knowing  the  conditions  which  are  favorable  to  fertility, 
and  particularly  those  conditions  which  are  known  to  act 
unfavorably  upon  the  breeding  functions, 
i  113 


114  THE   BREEDING   OF   ANIMALS 

110.  The  causes  of  sterility.  —  The  various  causes 1 
of  sterility  may  be  classified  as  anatomical,  physiological, 
pathological  or  psychological.     Sterility  in  the  male  may 
be  due  to  an  inability  to  perform  the  sexual  act,  which 
condition  is  known  as  impotence,  or  it  may  be  due  to  an 
inability  properly  to  develop  spermatozoa. 

111.  Causes  of  sterility  in  the  male.  —  The  male  may 
be  sterile  as  a  result  of  undeveloped  testicles  as  in  some 
ridglings,  where  the  testicles  are  retained  in  the  abdomen. 
The  ridgling  is  not  always  permanently  sterile  and  may 
be  fully  fertile,  but  the  failure  of  the  testicles  to  descend 
normally  from  the  abdominal  cavity  into  the  scrotum 
is  to  be  regarded  with  suspicion  by  the  breeder.     The 
only  way  to  determine  whether  a  particular  ridgling  is 
fertile  is  by  actual  trial.     There  is  no  medicinal  or  surgi- 
cal treatment  which  can  make  a  barren  ridgling  fertile. 

Bulls,  boars  and  stallions  which  are  fed  upon  a  generous 
ration  of  highly  nutritious  food  and  are  not  given  regular 
exercise  tend  to  become  over-fat,  arid  such  a  condition 
often  leads  to  fatty  degeneration  of  the  testicles  and  conse- 
quent sterility.  This  condition  is  recognized  by  all  suc- 
cessful breeders.  Breeding  males  that  have  proven 
themselves  of  great  merit  as  sires  and  are  not  intended 
for  exhibition  are  generally  and  wisely  maintained  on  a 
moderate  allowance  of  nutritious  food,  being  careful 
to  limit  the  amount  and  provide  some  means  for  exercise, 
thus  avoiding  the  almost  inevitable  fatty  degeneration 
of  the  reproductive  tissues  which  follows  long-continued 
high  feeding  combined  with  little  exercise.  An  example 
of  the  intimate  relation  of  these  factors  to  fertility  is  to 
be  observed  in  the  breeding  practices  of  many  modern 

1  See  "Diseases  of  the  Horse,"  U.  S.  Department  of  Agri- 
culture, 1907,  pp.  151-154. 


STERILITY  115 

owners  of  draft  stallions  as  compared  with  the  methods 
of  early  stallioners  in  the  newer  agricultural  sections  of 
the  United  States.  It  was  formerly  the  custom  to  drive 
or  ride  the  stallion  from  farm  to  farm,  thus  often  covering 
a  territory  of  100  to  200  square  miles.  Stallions  so  handled 
were  notoriously  sure  foal-getters  and  not  infrequently 
were  successful  in  getting  from  eighty-five  to  ninety-five 
per  cent  of  the  mares  in  foal.  The  modern  plan  of 
keeping  the  draft  stallion  in  high  condition  and  stand- 
ing him  for  service  at  one  barn,  thus  requiring  all  mares 
to  come  to  him,  has  undoubtedly  reduced  the  fertility 
of  draft  stallions.  It  is  no  unusual  event  for  a  draft 
stallion  so  managed  to  get  only  sixty  per  cent  of  mares  in 
foal,  while  seventy-five  per  cent  of  the  mares  in  foal  is 
regarded  by  some  stallioners  as  a  fair  average  for  stal- 
lions handled  in  this  manner.  The  fatty  degeneration 
of  the  vasa  deferentia  or  excretory  ducts  of  the  tes- 
ticles is  also  a  not  infrequent  cause  of  sterility  in  very 
fat  animals. 

Any  injury  or  deformity  of  the  penis  which  renders 
the  act  of  copulation  painful  or  impossible  is  to  be  included 
in  the  category  of  anatomical  causes  of  sterility.  In 
this  class  may  be  included  inflammation  or  ulceration 
of  the  mucous  membrane  enclosing  the  penis,  paralysis 
of  that  organ,  and  the  presence  of  tumors  on  the  penis 
itself  or  its  appendages.  Muscular  and  bone  diseases 
which  in  any  way  interfere  with  the  exercise  of  the  breed- 
ing function  are  causes  of  barrenness.  Spavin  or  ring 
bone  may  cause  the  stallion  such  inconvenience  and  dis- 
tress in  mounting  as  to  prevent  copulation  and  thus  indi- 
rectly be  a  cause  of  barrenness.  Similarly,  diseases  of  the 
muscles  of  the  back  and  loins  may  be  responsible  for 
sterility  in  certain  individuals.  Diseases  of  the  brain 


116  THE  BREEDING  OF  ANIMALS 

and  spinal  cord,  particularly  those  which  control  the 
act  of  coition,1  diabetes  and  albuminuria  are  tojbe  regarded 
as  causes  of  sterility. 

The  potency  of  the  semen  of  the  male  may  be  so  weak- 
ened by  too  frequent  services  by  the  stallion  as  to  result 
in  sterility.  The  number  and  frequency  of  services 
which  can  be  required  of  a  stallion  and  still  retain  the 
full  vitality  of  the  sperm-cells  varies  greatly  with  different 
individuals.  An  interesting  contribution  to  this  subject 
is  reported  by  Lewis : 2  A  draft  stallion  was  permitted 
one  cover  daily  for  nine  consecutive  days.  Samples 
of  the  semen  were  taken  to  the  laboratory  in  a  warm  steri- 
lized receptacle.  The  number  of  sperm-cells  to  the  cubic 
millimeter  in  the  semen  from  the  first  service  was  131,750. 
The  number  of  sperm-cells  decreased  daily  with  consider- 
able uniformity  until  the  ninth  service,  when  the  number 
suddenly  diminished  from  51,480  to  5840.  The  vitality 
of  the  spermatozoa  was  determined  by  maintaining  the 
fluid  at  a  uniform  temperature  and  determining  the  num- 
ber of  viable  sperm-cells  at  the  end  of  a  given  period. 
Thus  when  the  semen  was  kept  at  a  temperature  of  31 
to  35°  C.  it  was  found  that  five  per  cent  of  the 
cells  from  the  first  service  were  aliVe  after  nine  and  five- 
tenths  hours.  From  the  third  service  no  cells  were  alive 
after  six  hours.  From  the  sixth  service  no  cells  were 
alive  after  four  hours,  and  from  the  eighth  service  no  cells 
were  alive  after  three  hours.  In  a  second  test  a  grade 
stallion  was  bred  eleven  times  on  consecutive  days. 
The  author  summarizing  this  test  concludes  that : 3 
"  Approximately  the  vitality  of  the  cells  decreased  one- 

1  Comer,  "Diseases  of  the  Male  Generative  Organs,  "  1907. 

2  Lewis,  Oklahoma  Experiment  Station,  Bui.  96,  1911. 

3  See  Marshall,  "The  Physiology  of  Reproduction." 


STERILITY  117 

half  and  the  number  to  one-fifth  in  the  last  or  eleventh 
service  of  the  series  as  compared  with  the  condition  of 
the  semen  at  the  first  service."  Other  conditions  which 
are  to  be  regarded  as  sources  of  barrenness  are  incomplete 
erections,  premature  ejaculations,  fear  and  repugnance. 
The  inability  of  the  male  to  produce  fertile  semen  may 
be  a  congenital  condition  or  it  may  be  acquired  through 
some  of  the  causes  mentioned  in  this  chapter. 

112.  Sterility   in   the    female. —  The   failure    of   the 
female  to  produce  offspring  is  due  to  a  variety  of  causes. 
Some  of  these  are  inherent  and  cannot  be  successfully 
treated.     Such  animals  are  permanently  barren  and  of 
course  useless  for  breeding  purposes.     There  are  other 
causes  of  infertility  which  are  the  result  of  purely  tempo- 
rary circumstances,  and  these  may  often  yield  to  skillful 
treatment  by  man  and  valuable  animals  thus  become 
regular  breeders..    Some  of  the  more  important  causes 
of  sterility  which  are  temporary  and  which  may  yield 
to  treatment  are  mentioned  below. 

113.  Closure  of  the  cervix.  —  Mares  and  cows  often 
fail  to  become  pregnant  as  a  result  of  the  constriction  of 
the  muscles  forming  the  neck  of  the  womb.     This  spas- 
modic closure  of  the  cervix  prevents  the  passage  of  the 
semen  from  the  vagina  into  the  uterus,  and  the  fertiliza- 
tion of  the  egg  is  thus  prevented.     This  condition  is  more 
frequent  in  young  females  that  have  never  been  pregnant, 
but  is  not  uncommon  among  animals  that  have  previously 
given  birth  to  offspring.    This  condition  may  generally 
.be  successfully  treated  by  a  simple  operation  known  to 
the  stallioners  as  opening.     The  treatment  for  this  con- 
dition is  admirably  and  clearly  described  by  Law  1  as 
follows :    "  Spasmodic  closure  of  the  neck  of  the  womb 

1 "  Diseases  of  the  Horse,"  U.  S.  Department  of  Agriculture,  1907. 


118  THE   BREEDING   OF   ANIMALS 

is  common  and  is  easily  remedied  in  the  mare  by  dilata- 
tion with  the  fingers.  The  hand,  smeared  with  bella- 
donna ointment  and  with  the  fingers  drawn  into  the  form 
of  a  cone,  is  introduced  through  the  vagina  until  the  pro- 
jecting, rounded  neck  of  the  womb  is  felt  at  its  anterior 
end.  This  is  opened  by  the  careful  insertion  of  one  finger 
at  a  time,  until  the  fingers  have  been  passed  through  the 
constricted  neck  into  the  open  cavity  of  the  womb.  The 
introduction  is  made  with  a  gentle  rotary  motion,  and 
all  precipitate  violence  is  avoided,  as  abrasion,  laceration 
or  other  cause  of  irritation  is  likely  to  interfere  with 
the  retention  of  the  semen  and  with  impregnation.  If 
the  neck  of  the  womb  is  rigid  and  unyielding  from  the 
induration  which  follows  inflammation  —  a  rare  condi- 
tion in  the  mare,  though  common  in  the  cow  —  more 
force  will  be  requisite,  and  it  may  even  be  needful  to  incise 
the  neck  to  the  depth  of  one-sixth  of  an  inch  in  four 
or  more  opposite  directions  prior  to  forcible  dilation.  The 
incision  may  be  made  with  a  probe-pointed  knife,  and 
should  be  done  by  a  professional  man  if  possible.  The 
subsequent  dilatation  may  be  best  effected  by  the  slow 
expansion  of  sponge  or  seaweed  tents  inserted  into  the 
narrow  canal.  In  such  cases  it  is  best  to  let  the  wounds 
of  the  neck  heal  before  putting  to  horse." 

114.  Obstruction  of  Fallopian  tubes  resulting  from 
excessive  fatness.  —  In  excessively  fat  animals,  the 
Fallopian  tubes  may  become  mechanically  obstructed 
by  the  pressure  of  fat  tissue.  This  closure  of  the  tube 
makes  it  impossible  for  the  ova  to  descend  into  the  uterus, 
and  although  the  female  may  come  regularly  in  heat  and 
coition  occur,  the  animal  does  not  become  pregnant. 
This  condition  does  not  necessarily  involve  fatty  degen- 
eration of  the  reproductive  tissues,  but  may  be  associated 


PLATE  V.  —  Normal  healthy  uterus  of  sow.  a,  ovary ;  6,  fimbriated 
end  of  Fallopian  tube ;  c,  central  part  of  Fallopian  tube ;  d,  junction  of 
Fallopian  tube  with  horn  of  uterus ;  e,  uterine  folds  of  the  horns  of  uterus ; 
/,  body  of  uterus;  o,  position  of  "os  uteri" ;  vag.,  vagina  vulva,  bladder. 


PLATE  VI.  —  Sterility  in  the  sow.  Generative  organs  of  a  domestic 
sow,  illustrating  cystic  ovaries  which  in  this  case  resulted  in  complete 
sterility. 


STERILITY  119 

with  it.  It  is  of  course  not  possible  to  determine  by 
external  examination  of  the  live  animal  whether  failure 
to  breed  in  a  particular  case  is  due  to  mechanical  obstruc- 
tion of  the  Fallopian  tubes  or  to  other  causes.  It  is  often 
possible  to  overcome  this  difficulty  by  dieting  the  animal. 
Very  fat  animals  which  do  not  breed  should  be  placed 
upon  a  restricted  diet  which  will  cause  them  to  lose  weight 
regularly  until  they  have  regained  a  normal  breeding 
condition. 

115.  Other  causes  of  barrenness.  —  Other  conditions 
which  may  be  regarded  as  more  or  less  temporary  causes 
of  barrenness  are :  (a)  insufficient  food  supply,  causing 
emaciation  and  a  consequent  failure  of  the  sexual  organs 
to  mature  ova;  (6)  failure  of  the  animal  to  retain  the 
semen  of  the  male,  due  to  unusual  nervous  irritability 
of  the  female  sexual  organs ;  and  (c)  sudden  and  marked 
change  of  condition,  such  as  is  brought  about  by  the 
transportation  of  animals  from  one  continent  to  an- 
other. (Plates  V  and  VI.) 

Some  of  the  causes  and  treatment  of  sterility  have 
already  been  somewhat  fully  discussed  under  the  general 
subject  of  fertility.  A  mere  mention  of  some  of  the 
above  causes  of  sterility  indicates  the  treatment.  In 
many  cases  of  sterility  all  that  is  needed  is  to  remove 
the  cause.  The  nervous  irritability  of  the  female  sexual 
organs  seems  to  be  caused  by,  or  at  least  associated  with, 
an  unusual  flow  of  blood  to  the  generative  organs,  causing 
congestion.  This  condition  can  be  alleviated  sometimes 
by  exercising  the  female  even  to  the  point  of  exhaustion. 
It  is  a  well-known  fact  that  the  Arabs  were  in  the  habit 
of  riding  their  mares  to  exhaustion  just  before  mating 
with  the  stallion.  This  treatment  brought  about  a 
generally  relaxed  condition  of  the  whole  body  and  par- 


120  THE   BREEDING  OF  ANIMALS 

ticularly  of  the  reproductive  organs,  which  is  to  be  re- 
garded as  favorable  for  conception. 

The  importation  of  animals  from  foreign  countries 
often  results  in  temporary  barrenness.  This  condition 
seldom  or  never  becomes  permanent. 

116.  Sterility  from  fatty  degeneration.  —  The   main- 
taining of  animals  in  an  excessively  fat  condition  for  a 
long  period  of  time  will  eventually  result  in  fatty  degener- 
ation of  the  tissues.    When  this  condition  attacks  the 
ovaries,  it  frequently  causes  permanent  sterility.     Cer- 
tain foods  are  believed  to  hasten  fatty  degeneration  of  the 
reproductive  tissues.    Tanner 1  holds  that   "  this  fatty 
degeneration  of  the  ovaries  has  been  traced  to  the  use  of 
foods  rich  in  sugar.     I  have  reason  to  believe  that  the 
action  of  sugar  in  its  various  forms  is  most  important 
in  its  influence  upon  the  generative  system,  and  I  think 
there  is  just  cause  for  considering  that  any  animal  may 
by  its  use  be  rendered  incompetent  for  propagating  its 
species." 

117.  Sterility  caused  by  abortion.  —  Among  the  impor- 
tant causes  of  infertility  among  the  domestic  animals 
probably  none  is  responsible  for  so  many  failures  to 
produce    living    offspring    as   abortion.     Two   kinds    of 
abortion  are  recognized,  non-contagious  and  contagious. 
Non-contagious  abortion  may  result  from  a  variety  of 
causes  closely  associated  with  the  environment  of  the 
animal.     Law  2  gives  a  number  of  the  more  important 
causes  of  abortion  in  the  mare.     "  The  mare  may  abort 
by  reason  of  almost  any  cause  that  very  profoundly  dis- 

1  Tanner,  "The  Reproductive  Powers  of  the  Domestic  Ani- 
mals," Journal  of  the  Royal  Agricultural  Society,  vol.  1,  1865, 
p.  267. 

2  Law,  "Diseases  of  the  Horse,"  U.  S.  Department  of  Agri- 
culture, 1903. 


STERILITY  121 

turbs  the  system.  Hence  very  violent  inflammations 
of  important  internal  organs  (bowels,  kidneys,  bladder, 
lungs)  may  induce  abortion.  Profuse  diarrhea,  whether 
occurring  from  the  reckless  use  of  purgatives,  the  con- 
sumption of  irritants  in  the  food,  or  a  simple  indigestion 
is  an  effective  cause.  No  less  so  is  acute  indigestion 
with  evolution  of  gas  in  the  intestines  (bloating).  The 
presence  of  stone  in  the  kidneys,  uterus,  bladder  or  urethra 
may  induce  so  much  sympathetic  disorder  in  the  womb 
as  to  induce  abortion.  In  exceptional  cases  wherein 
mares  come  in  heat  during  gestation,  service  by  the 
stallion  may  cause  abortion.  Blows  or  pressure  on  the 
abdomen,  rapid  driving  or  riding  of  the  pregnant  mare, 
especially  if  she  is  soft  and  out  of  condition  from  idleness, 
the  brutal  use  of  the  spur  or  whip,  and  the  jolting  and 
straining  of  travel  by  rail  or  boat  are  prolific  causes. 
Bleeding  the  pregnant  mare,  a  painful  surgical  opera- 
tion, and  the  throwing  and  constraint  resorted  to  for  an 
operation  are  other  causes.  Traveling  on  heavy  muddy 
roads,  slips  and  falls  on  ice,  and  jumping  must  be  added. 
"The  stimulation  of  the  abdominal  organs  by  a  full  drink 
of  iced  water  may  precipitate  a  miscarriage,  as  may  expo- 
sure to  a  cold  rainstorm  or  a  very  cold  night  after  a  warm 
day.  Irritant  poisons  that  act  on  the  urinary  or  genera- 
tive organs,  such  as  Spanish  flies,  rue,  savin,  tansy,  cotton- 
root  bark,  ergot  of  rye  or  other  grasses,  the  smut  of 
maize  and  other  grain,  and  various  fungi  in  musty  fodder 
are  additional  causes.  Frosted  food,  indigestible  food 
and,  above  all,  green  succulent  vegetables  in  a  frozen 
state,  have  proved  effective  factors,  and  filthy  stagnant 
water  is  dangerous.  Low  condition  in  the  dam  and 
plethora  have  in  opposite  ways  caused  abortion,  and  hot, 
relaxing  stables  and  lack  of  exercise  strongly  induce  it. 


122  THE  BREEDING  OF  ANIMALS 

The  exhaustion  of  the  sire  by  too  frequent  service,  entail- 
ing debility  of  the  offspring  and  disease  of  the  fetus  or  of  its 
envelopes,  must  be  recognized  as  a  further  cause."  The 
symptoms  of  abortion  are  similar  to  those  of  approach- 
ing parturiti6n  (see  p.  75),  if  the  threatened  abortion 
occurs  during  the  later  stages  of  pregnancy.  Abortion 
may  occur  during  the  first  four  weeks  of  pregnancy  with- 
out any  very  marked  symptoms.  The  fact  of  abortion 
is  indicated  by  the  animal  again  coming  in  heat.  But, 
as  already  shown  in  cases  of  superfcetation,  the  occurrence 
of  heat  is  not  absolute  evidence  that  abortion  has  resulted. 
Ewart 1  has  called  attention  to  the  fact  that  the  mare 
is  far  more  apt  to  abort  at  certain  stages  of  gestation 
than  at  others.  He  regards  the  period  from  the  sixth 
to  the  ninth  week  as  one  during  which  the  mare  is  pecul- 
iarly susceptible  to  changes  in  her  environment  which 
may  have  a  tendency  to  cause  abortion.  This  is  due 
to  a  change  in  the  form  of  attachment  of  the  foetus  to  the 
uterus,  from  the  primitive  yolk  sac  to  the  more  permanent 
villi-.  "  At  the  end  of  the  third  week  of  gestation,  when 
the  reproductive  system  passes  through  one  of  its  periods 
of  general  excitement,  about  one-fourth  of  the  embryonic 
sac  probably  adheres  to  the  uterus ;  but  at  the  end  of  the 
sixth  week,  when  another  wave  of  disturbance  arrives, 
all  the  grappling  structures  are  at  one  pole.  Hence, 
there  is  probably  more  chance  of  the  embryo  '  slipping ' 
at  the  end  of  the  sixth  than  at  the  end  of  the  third  week. 
About  the  end  of  the  seventh  week  the  supply  of  nourish- 
ment by  means  of  the  yolk  sac  is  coming  to  an  end,  and 
there  is,  perhaps,  still  about  this  time  an  hereditary  tend- 
ency for  the  embryo  to  escape.  Unless  the  new  and  more 
permanent  nutritive  apparatus  is  provided,  unless  a 

1  Ewart,  quoted  by  Marshall,  loc.  cit.,  p.  615. 


STERILITY  123 

countless  number  of  villi  rapidly  sprout  out  from  the 
allantois,  the  embryo  will  die  from  starvation  during 
the  eighth  week,  and  in  a  few  days  be  discharged.  It 
may,  therefore,  be  taken  for  granted  that  there  is  a  cer- 
tain amount  of  danger  at  the  end  of  the  third  and  sixth 
weeks,  but  that  the  most  critical  period  is  about  the  end 
of  the  seventh  or  beginning  of  the  eighth  week ;  for  unless 
the  villi  appear  in  time,  and  succeed  in  coming  into  suffi- 
ciently intimate  relation  with  the  uterine  vessels,  the 
developmental  process  is  of  necessity  forever  arrested." 

Abortion  among  sheep  seems  to  be  largely  due  to  debili- 
tating conditions  due  to  insufficient  and  unsuitable  food, 
although  Heape 1  has  pointed  out  that  shearling  ewes 
are  more  apt  to  abort  than  those  of  maturer  age. 

118.  Contagious  abortion  and  sterility.  —  The  most 
insidious,  widespread  and  generally  important  cause  of 
sterility,  especially  among  cows,  is  due  to  a  germ  infection 
(Boot,  abortus)  which  is  recognized  under  the  terms  con- 
tagious, or  infectious  abortion.  It  is  found  oftener  in 
herds  of  dairy  cattle  than  among  beef  breeds,  not  because 
dairy  animals  are  more  susceptible  to  this  disease,  but 
because  they  are  generally  handled  in  such  a  manner  as 
to  provide  more  favorable  conditions  for  its  spread. 
Beef  breeds  are  generally  less  closely  housed  and  they 
are  more  frequently  permitted  to  calve  on  the  pastures, 
thus  avoiding  two  common  circumstances  favorable  for 
the  transmission  of  the  disease.  The  infection  is  carried 
chiefly  by  the  bull.  If  a  healthy  bull  is  permitted  to 
serve  a  cow  infected  with  the  germ  of  abortion,  he  will 
generally  transfer  the  infection  to  all  cows  which  later 
may  be  served  by  him.  The  disease  is  not  communicated 
to  any  important  extent  from  cow  to  cow  by  merely 

1  Heape,  "Abortion,  Barrenness  and  Fertility  in  Sheep." 


124  THE  BREEDING  OF  ANIMALS 

standing  side  by  side  in  the  same  barn.  The  Scottish 
Committee  appointed  to  investigate  abortion  found  that 
infection  might  be  carried  from  a  diseased  cow  to  a  healthy 
animal  by  inserting  a  small  wad  of  cotton  into  the  vagina 
of  a  diseased  cow  for  twenty  minutes  and  transferring 
this  to  the  vagina  of  a  healthy  pregnant  cow  or  sheep. 
Such  infection  invariably  caused  abortion  within  a  month.1 
The  specific  organism  Bacterium  abortus  is  probably  not 
the  only  germ  which  may  cause  abortion.  MacFadyean  2 
has  called  attention  to  the  very  great  increase  in  the 
sterility  of  cows  in  Prussia  and  Switzerland  during  recent 
years.  The  cause  of  this  sterility  has  been  ascribed  to  a 
disease  known  as  "  infectious  granular  vaginitis."  This 
affection  produces  an  acute  inflammation  of  the  vulva 
and  vagina  and  the  infection  is  spread  through  a  herd 
by  the  bull.  Law 3  holds  "  that  any  micro-organism 
which  can  live  in  or  on  the  living  membrane  of  the  womb 
producing  a  catarrhal  inflammation,  and  which  can  be 
transferred  from  animal  to  animal  without  losing  its 
vitality  or  potency  is  of  necessity  a  cause  of  contagious 
abortion." 

119.  Treatment  for  contagious  abortion.  —  The  con- 
tinuance of  contagious  abortion  is  generally  prolonged 
even  under  the  best  of  circumstances.  Treatment  may 
sometimes  be  very  successful,  and  again  any  form  of  treat- 
ment may  fail  to  make  any  lasting  impression  upon  the 
disease.  As  the  bull  is  the  chief  source  of  contagion,  the 
treatment  should  start  with  him.  Veterinarians  recom- 
mend that  the  sheath  and  external  genitals  of  the  bull 

1  Law,  "Diseases  of  Cattle,"  U.  S.  Department  of  Agriculture, 
1908. 

2  MacFadyean,    Journal    of  the  Royal    Agricultural    Society, 
1909,  p.  337. 

3  Law,  loc.  cit.,  p.  166. 


STERILITY  125 

be  thoroughly  disinfected  with  a  solution  of  bichloride 
of  mercury  1  to  2000  containing  one  per  cent  of  copper 
sulfate.  The  same  disinfectant  should  be  used  to  flush 
the  vagina  of  the  suspected  cows.  Nocard  1  recommends 
the  following  solution  for  cleansing  the  external  genitals, 
anus  and  tail  of  the  aborting  cow : 

Distilled  or  pure  rain  water       ....     2  gallons 

Hydrochloric  acid 2^  ounces 

Corrosive  sublimate 2\  drachms 

These  ingredients  should  be  thoroughly  mixed. 

In  Denmark,  according  to  Dalrymple,2  all  membranes 
and  the  foetus  are  buried  in  lime  and  the  internal  genital 
organs  of  the  cow  are  thoroughly  disinfected  with  a  one 
per  cent  solution  of  creolin  or  a  half  per  cent  solution  of 
lysol.  The  external  genitals  of  the  bull  and  of  cows  about 
to  be  bred  are  treated  with  the  same  solution. 

All  aborted  tissues  must  be  burned  and  the  premises 
thoroughly  disinfected.  This  treatment  is  uncertain 
and  often  unsuccessful.  A  breeder  will  generally  gain 
time  in  the  eradication  of  abortion  from  his  herd  by  insist- 
ing upon  never  using  a  contaminated  male  on  young  heifers 
bred  for  the  first  time  or  upon  cows  known  to  be  free  from 
the  disease.  All  infected  and  aborting  cows  should  be 
separated  absolutely  from  the  females  which  have  never 
aborted.  All  cows  known  to  be  free  from  the  disease 
should  be  covered  by  a  bull  also  known  to  be  free  from 
infection.  The  uninfected  herd  must  be  guarded  from 
infection  from  the  diseased  herd.  This  plan  will  even- 
tually build  up  a  clean  herd  and  no  other  method  so  far 
devised  is  certain  to  accomplish  this  desirable  result. 

1  Dalrymple,  "Veterinary  Obstetrics,"  p.  59. 

2  Loc.  cit. 


126  THE   BREEDING  OF  ANIMALS 

The  problem  of  treating  the  bull  and  cows  known  to 
be  infected  is  quite  distinct  from  the  building  up  of  a 
clean  herd.  Fortunately  this  infection  is  not  transmitted 
by  heredity  and  is  not  necessarily  spread  from  mother 
to  offspring  by  direct  infection.  It  is,  therefore,  possible 
for  a  breeder  to  retain  in  the  young  animals  from  the 
infected  herd  the  best  products  of  his  skill  and  experi- 
ence. When  a  cow  from  the  infected  herd  aborts,  all 
tissues  expelled  from  the  uterus  should  be  promptly 
burned  and  the  stall  thoroughly  disinfected  by  a  generous 
use  of  lime.  The  vagina  of  the  cow  should  be  disinfected 
with  the  solution  described  on  p.  125.  The  aborting 
cow  should  be  permitted  to  rest  at  least  six  months  before 
breeding  again.  The  prevention  of  abortion  in  a  cow 
already  pregnant  has  been  successfully  accomplished  in  a 
number  of  instances  by  internal  applications  of  carbolic 
acid.  Taylor's 1  successful  experiments  in  preventing 
impending  abortion  are  worthy  of  note.  A  description 
of  the  treatment  of  one  cow  is  typical  and  will  serve  as 
an  example  of  the  methods  which  were  generally  successful. 
A  grade  cow  four  years  old  that  had  aborted  the  previous 
year  and  was  known  to  be  infected  with  granular  vaginitis 
was  given  the  following  treatment:  At  the  beginning 
of  the  fourth  month  of  the  period  of  gestation  she  was 
given  200  cubic  centimeters  of  a  four  per  cent  solution 
of  carbolic  acid  in  her  feed.  The  dose  was  increased  to 
250  cubic  centimeters  the  fifth  month  and  to  300,  350  and 
400  cubic  centimeters  for  the  sixth,  seventh  and  eighth 
months  respectively.  This  cow  dropped  a  strong  healthy 
calf  at  the  end  of  the  normal  period  of  gestation.  A  sum- 
mary of  the  results  in  one  herd  treated  by  Taylor  shows 

1  Taylor,  Montana  Experiment  Station,  Bulletin  No.  90, 
1912. 


STERILITY  127 

that  in  1908  there  were  fifteen  per  cent  abortions,  in  1909 
twenty-five  per  cent,  in  1910  five  per  cent,  and  in  1911 
two-and-one-half  per  cent  of  abortions.  The  carbolic 
treatment  was  begun  in  December,  1909.  It  is  recom- 
mended that  infected  males  be  treated  in  the  same  manner.1 

120.  Diagnosis  of  contagious  abortion.  —  This  disease 
is  so  widespread  and  causes  such  serious  consequences 
when  once  well  established  in  a  herd  that  it  is  often  of 
the  greatest  importance  to  be  able  to  detect  its  presence 
in  animals,  even  those  which  are  not  at  the  time  pregnant. 
Various  attempts  have  been  made  with  greater  or  less 
success  to  secure  a  reliable  diagnostic  agent  which  would 
make  it  possible  for  the  breeder  to  know  which  animals 
in  his  herd  are  infected  with  the  germ  of  contagious  abor- 
tion and  thus  be  able  to  separate  the  infected  individuals 
from  those  which  are  healthy. 

The  first  substance  of  this  character  to  be  used  was 
similar  to  tuberculin  and  mallein.  The  name  of  "  abor- 
tin  "  was  given  to  this  substance  by  MacFadyean  and 
Stockman.  This  material  was  to  be  injected  into  the 
circulation  of  the  cows  of  a  herd.  The  infected  cows 
showed  a  considerable  rise  in  temperature  following  the 
infection.  The  healthy  cows  showed  but  little  or  no 
increase  in  temperature.  Briill2  at  Vienna,  after  testing 
this  method  on  a  large  number  of  cows,  concluded  that 
abortin  was  an  unreliable  diagnostic  agent  for  determining 
the  presence  of  contagious  abortion  in  cattle.  Other 
investigators  have  reported  similar  unfavorable  results 
from  the  use  of  this  material. 


1  See  also  Good,  Kentucky  Experiment  Station,  Bui.  No.  165 ; 
Surface,  Kentucky  Experiment  Station,  Bui.  No.  166  ;  MacNeal 
and  H.  W.  Mumford,  Illinois  Experiment  Station,  Bui.  No.  152. 

2  Briill,  "Berl.  Tierartzt  Woch.,"  Bd.  27,  pp.  721-727. 


128  THE   BREEDING   OF  ANIMALS 

In  cases  of  typhoid  fever,  the  so-called  agglutination 
test  was  found  to  be  a  fairly  reliable  agent  for  the  diagnosis 
of  this  disease.  In  1907-8,  Ginstead  in  Denmark  applied 
this  test  successfully  to  cows  suffering  from  contagious 
abortion.  Later  MacFadyean  and  Stockman  l  published 
the  results  of  a  limited  number  of  investigations,  report- 
ing unfavorably  upon  this  method.  Later  Holth  and 
Wall,2  after  an  extensive  series  of  investigations  involving 
hundreds  of  cows,  concluded  that  the  agglutination  test 
was  a  reliable  diagnostic  agent  but  probably  subject  to 
larger  error  than  the  complement  fixation  test. 

121.  The  complement  fixation  test.3  —  Neither  the 
abortin  nor  the  agglutination  test  has  proven  entirely 
satisfactory  under  all  circumstances.  The  most  reliable 
test  now  available  is  the  complement  fixation  test.4 
Connaway  of  the  Missouri  Experiment  Station  says, 
"  This  test  has  been  found  very  reliable  as  a  diagnostic 
method  in  contagious  abortion.  The  result  of  the  test 
on  some  infected  herds  shows  that  in  old  infected  herds 
the  per  cent  of  re-acting  animals  runs  from  60  to  90  per 
cent."  This  is-  a  highly  complicated  and  difficult  test 
to  make,  but  will  with  practical  certainty  cause  a  reaction 
in  cows  that  have  been  infected.  Cows  that  have  aborted 
may  develop  an  immunity  to  this  disease,  and  when  this 
has  occurred  the  complement  fixation  test  cannot  be 
used  to  distinguish  between  those  cows  which  will  abort 

1  MacFadyean  and  Stockman,  "Report  of  the  Departmental 
Committee   to  inquire  into   Epizootic   Abortion,"   Pt.    I,   and 
Appendix,  London,  1909. 

2  "Berl.  Tierartzt  Woch.,"  Bd.,  pp.  686-688,  1909. 

3  See  Surface,  Kentucky  Exp.  Sta.  Bui.  No.  166;    MacNeal 
and  Mumford,  Illinois  Exp.  Sta.  Bui.  No.  152 ;  Russell,  Science, 
N.  S.,  vol.  34,  p.  494,  1911 ;  Wisconsin  Research,  Bui.  No.  24, 
1912. 

4  Missouri  Experiment  Station,  Bui.  131,  p.  486. 


STERILITY  129 

and  those  which  are  immune.  The  great  value  of  this 
lies  in  the  fact  that  the  aborting  cows  may  be  entirely 
separated  from  the  healthy  members  and  eventually 
by  this  separation  the  disease  may  be  entirely  eliminated 
from  the  herd. 

122.  Sterility  of  free-martins.  —  The  birth  of  twins 
among  cattle  is  frequent.  When  a  cow  gives  birth  to 
twins,  one  a  female  and  the  other  a  male,  the  female  is 
called  a  free-martin  and  is  generally  sterile.  So  far  as 
known,  this  condition  does  not  exist  among  any  other 
known  species  of  animal.  Among  sheep,  for  example, 
where  twins  are  very  common,  the  female  twin  born  with 
a  male  may  be  even  more  fertile  than  the  single  born 
lamb.  No  case  of  sterility  among  human  twins  has  ever 
been  recorded  where  the  sterile  condition  was  believed 
to  be  due  to  the  fact  that  one  twin  was  a  male  and  the 
other  a  female.  Among  cattle  where  both  twins  are  of 
the  same  sex  both  are  fully  fertile.  This  is,  therefore, 
a  remarkable  biological  fact  which  it  is  difficult  to  explain. 
Morse1  reports  that  Dr.  Luer  found  113  cases  of  twins, 
one  a  male  and  the  other  a  female,  in  the  records  of  the 
East  Prussian  Holland  Herd  Book.  Of  this  number  all 
the  females  were  sterile  except  six. 

The  author  has  examined  a  considerable  number  of 
free-martins  and  in  every  case  of  sterility  the  female 
reproductive  organs  have  been  imperfectly  developed. 
One  case  examined  is  typical.  A  grade  Aberdeen  Angus 
had  every  external  appearance  of  a  female.  The  loca- 
tion and  form  of  the  external  genital  organs  was  that  of 
a  true  female.  There  were  only  two  peculiarities  which 
were  visible  externally.  A  tuft  of  long  hair  resembling 
the  growth  on  the  sheath  of  the  bull  grew  from  the  lower 

1  Morse,  Breeder's  Gazette,  vol.  64,  p.  346. 


130  THE   BREEDING   OF   ANIMALS 

extremity  of  the  vulva.  The  mammary  glands  were 
very  small  and  but  little  developed  and  resembled  more 
the  rudimentary  mammary  glands  of  a  bull  than  the 
normal  glands  of  a  cow.  At  two  years  of  age  this  sup- 
posed cow  had  never  come  in  heat.  She  was  permitted 
to  run  in  the  same  paddock  with  two  mature  bulls  for  a 
period  of  six  months,  but  never  came  in  heat.  This 
animal  was  slaughtered  and  the  reproductive  organs 
removed  for  examination.  It  was  found  that  the  animal 
had  a  vulva  and  a  very  short  vagina-like  organ  ending 
in  a  blind  sac.  No  uterus,  Fallopian  tubes  or  ovaries 
were  found.  There  was  also  found  a  rudimentary  penis. 
It  seems  probable  that  sterile  free-martins  are  imperfect 
males  or  hermaphrodites.  It  is  not  possible  at  this  time 
to  give  any  satisfactory  explanation  of  why  there  should 
exist  a  greater  tendency  to  hermaphroditism  when  twins 
of  different  sex  are  born  than  twins  of  identical  sex.  It 
is  still  more  difficult  to  explain  why  this  phenomenon 
should  occur  exclusively  among  cattle.  It  is  possible 
that  the  explanation  of  this  phenomenon  is  associated  in 
some  way  with  the  production  of  identical  twins,  but 
this  does  not  offer  any  satisfactory  explanation  of  why 
this  strange  occurrence  should  be  found  in  the  bovine 
species  alone. 


CHAPTER  VII 
HEREDITY 

THE  characteristics  of  the  individual  are  determined 
by  heredity  and  development.  What  an  animal  may 
become,  depends  on  the  heritage  received  from  its 
ancestors.  No  organic  being  can  be  developed  beyond 
the  limits  imposed  upon  it  by  its  inheritance.  A  favor- 
able environment  and  good  training  will  permit  the 
individual  to  achieve  the  full  limit  of  its  possibilities, 
but  no  amount  of  training  and  no  combination  of  favor- 
able circumstances  can  ever  lift  the  individual  above  the 
inheritance  which  it  has  gained  through  its  parents. 
The  trotting  horse  may  have  inherited  the  capacity  to 
trot  a  mile  in  two  minutes,  but  if  its  development  has 
been  arrested  by  insufficient  food  and  an  unfavorable 
climate,  and  no  attempt  has  been  made  to  develop  its 
inherent  ability  to  go  fast,  it  can  never  achieve  the  full 
measure  of  its  possibilities.  It  is  also  true  that  if  a  horse 
has  not  inherited  from  a  line  of  trotting  ancestors  the 
ability  to  go  fast  at  the  trot,  no  amount  of  training  and 
no  system  of  feeding  can  develop  the  animal  to  a  point 
where  it  will  be  able  to  trot  a  mile  in  two  minutes. 

Heredity  then  represents  what  an  animal  really  is  or 
can  become.  The  individual  cannot  in  any  manner  or 
to  any  extent  influence  its  own  heredity.  An  animal's 
inheritance  is  determined  by  its  ancestors.  The  indi- 

131 


132  THE   BREEDING  OF  ANIMALS 

vidual  may  profoundly  influence  its  development  through 
seeking  a  favorable  environment  and  through  habitual 
use  or  disuse  of  its  inherited  tendencies. 

123.  Development.  —  The  full  realization  of  the  in- 
herited capacities  of  an  animal  is  accomplished  through 
its    environment    and    training.     The    most    important 
factors  concerned  in  the  environment  of  an  animal  are 
food  and  climate,  and  these  acting  upon  the  inherited 
qualities  of  the  animal  may  profoundly  influence  the 
actual  characteristics  of  the  individual.     In  order  that 
the  inherent  characteristics  of  any  organic  being  may 
attain  to  full  development,  a  sufficient  supply  of  food 
must  be  available.     When  food  is  scarce,  the  individual 
may  be  unable  to  develop,  and  what  it  may  ultimately 
become,    may   be   greatly   influenced    by   this    lack    of 
food.    A  full  and  sufficient  food  supply  may  cause  the 
individual  to  develop  beyond  the  average  condition  of 
the  species,  particularly  if  the  average  environment  does 
not  furnish  a  generous  supply  of  food. 

The  training  of  the  individual,  likewise,  is  an  important 
factor  in  determining  its  ultimate  development.  Any 
function  of  an  animal  which  is  not  exercised  may  retro- 
grade or  in  some  .cases  practically  disappear.  The 
milking  function  in  domestic  cattle  is  a  good  example  of 
the  influence  of  both  development  and  exercise  or  train- 
ing. The  highly  developed  dairy  breeds  of  cattle,  when 
generously  fed  and  carefully  milked,  produce  very  much 
more  milk  than  their  wild  ancestors.  Individual  cows 
of  modern  dairy  breeds,  if  starved  and  carelessly  milked 
or  neglected,  will  fail  to  develop  the  highly  specialized 
milking  function. 

124.  Heredity  defined.  —  In  much  of  the  literature 
of  biology  pertaining  to  heredity,  there  is  a  lack  of  definite- 


HEREDITY  133 

ness  in  the  use  of  terms.  The  literature  of  animal-breed- 
ing is  still  less  exact  in  its  terminology.  It  seems  impor- 
tant, therefore,  that  in  the  very  beginning  we  should  have 
as  clear  a  conception  as  possible  of  the  definitions  of 
heredity  which  have  been  proposed.  Heredity  is  the 
organic  relation  existing  between  an  individual  and  its 
ancestors.  It  is  the  continuous  biological  thread  connect- 
ing generations  of  organic  beings.  Heredity  is  "  organic 
resemblance  based  on  descent. "  1  Thomson  2  has  defined 
heredity  as  "  the  organic  or  genetic  relation  between 
successive  generations."  "  Understood  in  its  entirety," 
says  Herbert  Spencer,3  "  the  law  is  that  each  plant  or 
animal,  if  it  reproduces,  gives  origin  to  others  like  itself ; 
the  likeness  consisting,  not  so  much  in  the  repetition  of 
individual  traits  as  in  the  assumption  of  the  same  general 
structure."  "  The  transference  of  similar  characters 
from  one  generation  of  organisms  to  another,  a  process 
effected  by  means  of  the  germ-cells  or  gametes."  4  "  By 
inheritance,"  says  Lock,5  "  we  mean  those  methods  and 
processes  by  which  the  constitution  and  characteristics 
of  an  animal  or  plant  are  handed  on  to  its  offspring,  this 
transmission  of  characters  being,  of  course,  associated 
with  the  fact  that  the  offspring  is  developed  by  the  pro- 
cesses of  growth  out  of  a  small  fragment  detached  from 
the  parent  organism."  Another  definition  of  heredity 
is  that  it  is  the  tendency  of  the  offspring  to  be  like  the 
parents.  There  exists  a  definite  organic  resemblance  or 

1  Castle,  "  Heredity  in  Relation  to  Evolution  and  Animal 
Breeding." 

2 Thomson,  "Heredity"  (1908),  p.  13. 

3  Herbert  Spencer,  "  Principles  of  Biology,"  vol.  I,  p.  301. 

'4  R.  H.  Lock,  "  Recent  Progress  in  the  Study  of  Variation, 
Heredity  and  Evolution,"  1906,  p.  292. 

5Loc.  cit.,  p.  1. 


134  THE  BREEDING   OF  ANIMALS 

relation  between  parents  and  offspring.  This  relation  is 
a  universal  biological  phenomenon  and  is  called  heredity. 
There  exists  a  continuous  line  of  descent  from  generation 
to  generation.  The  mechanism  of  heredity  is  to  be  found 
in  the  protoplasm  of  the  germ-cells.  The  stream  of 
descent  is  from  germ-cell  to  germ-cell.  The  soma-  or 
body-cells  constitute  in  a  sense  only  a  temporary  abiding 
place  for  the  germ-plasm. 

125.  Heredity  and  variation  not  antagonistic.  —  It  is 
not  stating  the  facts  correctly  to  maintain  that  the  tend- 
ency of  offspring  to  be  like  the  parent,  which  we  call 
heredity,  is  opposed  by  the  universal  tendency  of  organ- 
isms to  vary.     These  are  but  two  phases  of  the  same 
phenomenon.     "Living    beings    do    not    exhibit    unity 
and  diversity,"  says  Brooks,   "  but  unity  in  diversity. 
These  are  not  two  facts  but  one.     The  fact  is  the  indi- 
viduality in  kinship  of  living  beings.     Inheritance  and 
variation  are  not  two  things  but  two  imperfect  views 
of  a  single  process."    There  is  a  sense,  of  course,  in  which 
variation  is  opposed  to  heredity.     It  is  conceivable  that 
recombinations  of  characters  may  occur  in  the  germinal 
substance,  and  these  new  combinations  may  cause  such 
modification  of  characters  already  present  that  the  new 
organism  may  be  radically  changed. 

Heredity  is  the  genetic  relation  of  parents  and  offspring. 
On  the  average  the  offspring  will  be  like  the  parents. 
But  this  relation  admits  of  variations  within  more  or  less 
definitely  prescribed  limits.  The  offspring  have  an 
individuality  all  their  own,  but  this  does  not  preclude  the 
existence  of  a  genetic  continuity  which  is  the  common 
heritage  of  parents  and  offspring. 

126.  The   kinds   of   heredity.  —  Every   individual   is 
the  result  of  a  union  of  the  germ-plasm  of  two  individuals. 


HEREDITY  135 

The  evidences  of  this  dual  origin  are  not  always  exhibited 
in  the  same  manner.  In  some  individual  offspring  the 
characters  of  one  parent  may  predominate,  in  others 
the  parental  characters  seem  to  blend  so  successfully 
that  often  the  child  differs  from  either  parent,  while  in 
still  others  the  characters  of  both  parents  appear  in  the 
offspring  with  apparently  equal  force  but,  instead  of  blend- 
ing, the  characteristics  of  the  parents  appear  clearly  as 
distinct  and  easily  recognizable  qualities.  These  methods 
of  transmission  were  called  by  Galton,  blending,  alternate 
and  particulate  inheritance. 

127.  Blending  inheritance.  —  In  this  type  of  inherit- 
ance the  characters  of  the  offspring  represent  a  blending 
or  intermingling  of  the  characters  of  the  two  parents. 
Stature  in  man  may  and  often  does  represent  the  blend- 
ing of  the  statures  of  the  two  parents.     The  stature  of 
the  son  or  daughter  is  taller  than  the  shorter  parent,  but 
falls  short  of  that  of  the  taller  parent.     When  a  rela- 
tively small  mare  is  mated  with  a  heavy  draft  stallion, 
the  resulting  offspring  is  never  so  large  as  the  sire  nor  so 
small  as  the  dam,  but  represents  an  approach  to  a  mean 
between    the    two.     Another    example   of   blended    in- 
heritance  is  to  be  observed    in   the    cross-bred    lambs 
resulting  from  the  union  of  a  sire  of  the  coarse  wool  type 
and  a  dam  belonging  to  the  fine  wool  or  Merino  breed. 
The  lambs  of  such  a  cross  are  covered  with  wool  which  in 
respect  to  density,  length  of  staple  and  fineness  of  fiber 
represents  a  blending  of  the  characters  of  the  parents. 

In  some  cases  of  supposed  blending  inheritance,  the 
characters  have  been  observed  to  follow  the  law  of  domi- 
nance and  segregation  discovered  by  Mendel. 

128.  Alternative  inheritance.  —  A  character  may  be 
transmitted  intact  from  one  parent  directly  to  the  off- 


136  THE  BREEDING  OF  ANIMALS 

spring  without  apparent  modification  by  the  other  parent. 
In  this  type  of  inheritance  one  parent  seems  to  possess  a 
predominating  influence  in  determining  the  characteristics 
of  the  offspring.  Many  examples  of  this  type  of  heredity 
are  to  be  observed  among  the  domestic  animals.  The 
white  face  of  the  Hereford  breed  of  cattle  is  invariably 
transmitted,  even  when  one  parent  belongs  to  a  widely 
different  breed.  The  quality  of  speed  in  horses  is  un- 
doubtedly transmitted,  sometimes  in  accordance  with 
Galton's  alternative  inheritance.  Fecundity  in  the  do- 
mestic fowl  has  been  shown  by  Pearl  to  be  transmitted 
through  the  male.  The  hen  inherits  fecundity  directly 
from  the  sire.  The  ability  to  lay  a  large  number  of  eggs 
is  not  transmitted  from  the  mother  to  the  immediate 
female  offspring,  but  to  her  male  offspring. 

"  Hence  if  the  daughters  of  high  producing  hens  are 
selected,  one  does  not  get  in  them  the  high  productiveness 
of  the  mother.  It  is  her  sons  that  inherit  the  character, 
although  they  cannot  show  it  except  in  their  offspring."  1 

129.  Participate  or  mosaic  inheritance.  —  The  char- 
acters of  the  parents  are  often  transmitted  in  such  a 
manner  that  they  are  not  in  any  sense  blended  but  appear 
rather  as  a  mosaic.  The  color  character  is  frequently 
inherited  as  a  mosaic.  A  very  good  example  of  this 
kind  of  inheritance  is  seen  in  the  Holstein  Friesian  breed 
of  cattle.  This  breed  is  black  and  white,  these  colors 
appearing  in  definite,  clearly  defined  areas  and  not  blend- 
ing. The  Holstein  Friesian  breed  was  originated  by 
crossing  a  black  breed  and  a  white  breed  of  cattle.  The 
colors  black  and  white  in  other  animals  seem  to  behave 
in  a  similar  manner.  When  white  hogs  are  mated  with 
black,  the  offspring  are  always  spotted.  Recently  it 

1  Morgan,  "Heredity  and  Sex,"  p.  213. 


HEREDITY  137 

has  been  suggested  that  participate  inheritance  is  in 
reality  true  alternative  inheritance  in  which  the  mosaic 
result  is  caused  by  the  absence  of  the  factor  for  uniform- 
ity.1 

130.  Mendelian  inheritance.  —  Progress  in  the  investi- 
gation of  breeding  problems  has  come  through  statistical 
investigations,  by  cytological  studies  of  the  germ-cells 
themselves,  and  by  experimental  breeding.  Each  of 
these  methods  has  contributed  evidence  of  value  in  the 
direction  of  a  more  definite  understanding  of  the  prin- 
ciples of  heredity.  In  recent  years  experimental  breeding 
has  contributed  very  materially  to  our  knowledge  of 
the  science  of  heredity.  Improvements  in  the  technique 
of  cell  studies  has  supplemented  the  results  obtained  by 
experimental  breeding.  It  is  a  significant  fact  that  the 
hypotheses  based  upon  experimental  breeding  agree  in 
many  important  particulars  with  those  derived  from 
minute  investigations  of  the  origin  and  development  of 
'the  germ-cells. 

Perhaps  the  most  remarkable  series  of  investigations 
in  experimental  breeding  were  those  carried  on  by  Johann 
Gregor  Mendel,  an  Austrian  monk.  These  interesting 
investigations  gave  a  new  impetus  to  the  study  of  theoreti- 
cal heredity  and  particularly  to  the  practical  improve- 
ment of  plants  and  animals.  The  investigations  of  Mendel 
were  first  published  in  1865  and  over  twenty  years  later 
were  again  published  in  the  Transactions  of  the  Natural 
History  Society  of  Briinn.  No  attention  was  given  to  this 
important  contribution  to  the  science  of  breeding,  and 
even  Na'geli,  a  former  teacher  of  Mendel,  to  whom  the 
results  were  submitted,  failed  to  recognize  their  funda- 
mental significance.  It  was  not  until  the  year  1900 

1  Walter,  "Genetics,"  p.  164. 


138  THE   BREEDING   OF  ANIMALS 

that  three  great  investigators,  De  Vries  in  Holland,  Von 
Tschermak  in  Austria,  and  Correns  in  Germany,  simul- 
taneously discovered  the  published  results  of  Mendel  and 
recognized  their  great  fundamental  importance. 

131.  The  experiments  of  Mendel.  —  Mendel  selected 
for  his  experiments  the  common  garden  pea.  It  is  not 
certain  that  he  fully  recognized  the  wisdom  of  making 
such  selections  as  were  finally  made  for  his  work,  but  at 
any  rate  he  selected  two  varieties  of  peas  differing  in  a 
simple  character  but  each  firmly  fixed  in  the  parent 
variety.  The  peas  were  also  self -fertilizing,  and  accidental 
mixture  by  cross  fertilization  was  thus  avoided.  The 
characters  selected  by  Mendel  were  "  purple  or  white 
flowers,"  "yellow  or  green  cotyledons,"  and  "  round  or 
wrinkled  seeds."  He  found  that  all  of  these  characters 
were  firmly  fixed  and  bred  true.  These  varieties  were 
crossed  and  the  progeny  were  bred  pure  for  many  suc- 
ceeding generations. 

He  decided  upon  the  simple  character  of  color  and* 
selected  a  green  seeded  and  yellow  seeded  variety.  Recip- 
rocal crosses  were  made,  and  from  each  cross  the  result- 
ing peas  were  all  yellow.  Because  the  yellow  color  in 
the  cross  appeared  in  every  case,  he  called  it  the  dominant 
character;  and  the  green  color  which  did  not  appear  in 
the  first  generation  was  called  a  recessive  character. 

All  the  yellow  seeds  of  the  first  generation  resulting 
from  the  original  cross  were  planted.  In  the  second 
generation  Mendel  discovered  that  both  green  and  yellow 
seeds  appeared.  In  calculating  the  relative  proportion 
of  the  two  colors,  he  found  that  about  one-fourth  of  the 
seeds  were  green  and  the  remaining  three-fourths  yellow. 
The  green  seeds  and  yellow  seeds  were  planted  separately 
and  it  was  found  that  the  green  seeds  produced  only 


HEREDITY  139 

green  seeds.  They  were  planted  for  several  generations 
and  always  came  true,  showing  no  yellow  character. 
When  the  yellow  seeds  were  planted,  however,  Mendel 
found  that  a  certain  proportion  of  the  yellow  seeds  had 
both  green  and  yellow  offspring  and  a  certain  proportion 
had  only  yellow  offspring.  The  latter  remained  fixed 
and  true  in  character  when  bred  for  several  generations. 
The  results  of  these  investigations  carried  through 
many  generations  indicated  that  there  was  a  certain 
mathematical  ratio  traceable  in  the  offspring  resulting 
from  the  crossing  of  these  two  distinct  varieties  of  peas. 
In  these  results  Mendel  found  that  in  the  first  genera- 
tion the  dominant  character  (yellow  seed)  appeared  to 
the  exclusion  of  the  green  color.  In  the  second  genera- 
tion he  found  that  25  per  cent  of  the  offspring  were  green 
and  75  per  cent  apparently  yellow.  If  the  green  peas 
were  planted,  they  produced  only  green  peas,  but  when 
the  yellow  peas  were  planted,  they  produced  25  per  cent 
pure  yellow,  50  per  cent  mixed  or  hybrid  (yellow  and 
green),  and  25  per  cent  pure  green.  The  pure  yellows 
and  pure  greens  continued  to  breed  true,  but  the  50  per 
cent  "  hybrid  "  peas  continued  to  split  up  in  each  genera- 
tion in  the  proportions  of  25  per  cent  pure  green,  25  per 
cent  pure  yellow,  and  50  per  cent  hybrid. 

132.  The   law   of   dominance.  —  From   these   results 
Mendel  formulated  the  law  of  dominance,  which  is  that 
when  two  contrasting  characters  are  bred  together  the 
offspring  in  the  first  (Fi)  generation  will  all  exhibit  the 
dominant  character. 

133.  The  law  of  segregation.  —  When  the  individuals 
comprising  the  first  generation  are  interbred,  the  resulting 
offspring  (F2  generation)  will  possess  the  characters  in 
the  proportion  of  three  of  the  dominant  character  to  one 


140 


THE   BREEDING   OF  ANIMALS 


of  the  recessive.  The  recessive  character  is  pure  and  will 
breed  true.  The  individuals  possessing  the  dominant 
character  will  be  made  up  of  one-third  pure  dominants 
and  two-thirds  hybrid  dominants  in  which  the  recessive 


Dominant 


Recessive 


G( green) 


Y(G)  (fytrrf  ye//ow) 


(pure  ye/low)  YY          2. Y(d)  QG  (pure  green) 


YY        YY 


FIG.  16.  —  Diagram  illustrating  mendelian  inheritance  of  yellow  and 
green  characters  in  the  garden  pea. 

character  will  reappear  in  the  next  generation.  This  may 
be  more  clearly  shown  in  the  preceding  diagram  (Fig.  16). 
Mendel's  hypothesis  affirms  that  when  animals  or 
plants  of  contrasted  characters  are  bred  together,  these 
characters  do  not  blend  in  the  germ-cells  of  the  offspring. 


HEREDITY  141 

Fifty  per  cent  of  the  germ-cells  will  contain  the  dominant 
character  and  fifty  per  cent  the  recessive  character.  This 
is  true  of  both  male  and  female  germ-cells. 

134.  Unit  characters.  —  Mendel's  theory  presupposes 
the  existence  of  unit  characters,  so-called  because  they 
are  transmitted  as  independent  units.     There  exist  in 
every  organic  being  a  very  large  number  of  unit  char- 
acters, and  these  may  be  determined  by  experimental 
breeding.     Up  to  the  present  time  a  relatively  small 
number  of  unit  characters  have  been  definitely  differ- 
entiated and  described,  but  our  knowledge  in  this  direc- 
tion is  being  rapidly  extended. 

135.  Gametic  purity.  —  In  one  stage  of  maturation 
of  the  male  and  female  germ-cells,  the  nucleus  of  each 
contains  but  half  the  normal  number  of  chromosomes 
characteristic  of  the  species.    This  is  the  final  stage  in 
the  maturation  process  before  fertilization  takes  place. 
The  germ-cells  in  this  stage  are  called  gametes.    The 
fertilized  egg-cell  which  results  from  the  union  of  a  ma- 
ture sperm  and  egg-cell   (gametes)   is  called   a  zygote 
(fertilized  egg-cell).    The  zygote,  therefore,  contains  the 
normal  number  of   chromosomes   characteristic   of   the 
species,  one-half  derived  from  the  egg  and  one-half  from 
the  sperm-cell.     Gametic  purity  is  a  term  used  to  desig- 
nate the  discontinuous  nature  of  unit  characters.    The 
gamete  in  Mendel's  pea  contains  the  factor  necessary  for 
the  production  of  yellow  seeds,  or  it  does  not.1 

The  terms  homozygous  and  heterozygous  were  pro- 
posed by  Bateson  to  designate  the  fundamental  consti- 
tution of  the  germ-cells  in  respect  to  inherited  characters. 
"  An  individual  is  said  to  be  homozygous  for  a  given 

1  Darbishire,  "Breeding  and  the  Mendelian  Discovery," 
p.  217. 


142  THE   BREEDING   OF   ANIMALS 

character  when  it  has  been  formed  by  two  gametes  each 
bearing  the  character,  and  all  the  gametes  of  a  homozygote 
bear  the  character  in  respect  of  which  it  is  homozygous. 
When,  however,  the  zygote  is  formed  by  two  gametes  of 
which  one  bears  the  given  character  while  the  other  does 
not,  it  is  said  to  be  heterozygous  for  the  character  in 
question,  and  only  half  the  gametes  produced  by  such  a 
heterozygote  bear  the  character.  An  individual  may  be 
homozygous  for  one  or  more  characters,  and  at  the  same 
time  may  be  heterozygous  for  others."  1 

The  conception  of  "  gametic  purity "  as  originally 
stated  requires  some  modification.  It  is  no  longer  held 
that  characters  are  transmitted  as  units,  but  rather  the 
factors  which  combine  to  form  characters.  The  factors 
are  so  far  purely  imaginary. 

When  mendelism  was  first  seriously  considered,  there 
was  no  doubt  among  its  most  enthusiastic  exponents 
that  the  characters  existed  in  a  pure  unmixed  state  in 
the  gamete.2 

136.  Application  of  Mendel's  law.  —  Can  the  practical 
breeder  apply  the  principles  of  heredity  embodied  in 
Mendel's  law  to  the  improvement  of 'the  domestic  ani- 
mals ?  The  domestic  animals  are  valued  by  man  because 
of  certain  desirable  characteristics  which  they  possess. 
These  characteristics  are  clearly  recognized  by  the  breeder. 
The  meat  animal  is  produced  because  it  is  endowed  with 
certain  qualities  which  give  it  a  special  value  either  to 
the  consumer  or  the  producer.  The  dairy  cow  is  highly 
prized  because  she  has  the  ability  of  producing  large 
quantities  of  milk,  cream  or  cheese.  The  horse  is  the 
burden-bearer.  Its  value  depends  on  the  amount 

1  Punnett,  "  Mendelism,"  1913,  p.  28. 

*See  Castle,  "  General  Heredity,"  vol.  V,  No.  3,  p.  93. 


HEREDITY  143 

of  energy  it  can  develop  either  in  tractive  power  for'pull- 
ing  heavy  loads  or  in  the  form  of  speed  or  graceful  action 
for  the  pleasure  of  the  owner.  Other  animals  are  main- 
tained in  a  state  of  domestication  for  other  values  of 
various  kinds  which  contribute  to  the  food,  clothing  or 
pleasure  of  man.  In  a  sense  the  producer  of  live-stock 
may  be  compared  to  a  manufacturer  who  employs  capital, 
labor,  raw  materials  and  efficient- machines  for  the  pro- 
duction of  more  desirable  and  concentrated  products. 
In  this  comparison  the  raw  materials  are  the  grain,  hay 
and  grass ;  and  the  efficient  machine  is  the  animal.  The 
farmer's  success  and  the  interests  of  the  consumer  as 
well  are  greatly  dependent  upon  the  efficiency  of  this 
animal  machine.  Can  Mendel's  law  be  utilized  in  the 
efforts  of  the  breeder  to  increase  the  efficiency  of  animals  ? 
If  so,  what  does  the  breeder  need  to  know  in  order  to 
utilize  the  law  of  Mendel  in  further  enhancing  the  value 
of  the  prevailing  types  of  domestic  animals  ? 

137.  The  complexity  of  animal  characters.  —  It  must 
be  recognized  in  the  beginning  that  the  qualities  which 
are  commonly  mentioned  by  the  breeder  as  highly  desir- 
able are  generally  the  result  of  a  combination  of  many 
characters.  These  combinations  do  not  behave  as  simple 
unit  characters.  One  of  the  first  steps  in  the  application 
of  Mendel's  hypothesis  to  practical  breeding  must  be  to 
analyze  the  valuable  qualities  of  animals  and  determine 
as  far  as  possible  the  unit  characters.  It  is  probably 
true  that  some  combinations  will  behave  in  transmission 
in  the  same  manner  as  simple  unit  characters.  But  if 
there  are  complex  characters  which  behave  in  this  manner 
they  must  be  determined  by  careful  investigation.  When 
the  qualities  of  an  animal  have  been  differentiated  and 
their  behavior,  in  transmission  determined,  then  the  prac- 


144  THE  BREEDING  OF  ANIMALS 

tical  'breeder  may  base  his  breeding  methods  upon  the 
principles  of  segregation  and  dominance  which  are  founda- 
tion stones  in  the  theory  of  mendelian  inheritance. 

It  will  also  be  important  to  remember  that  to  utilize 
the  mendelian  principle  in  the  breeding  of  animals,  the 
breeder  must  be  dealing  with  contrasting  characters. 
In  the  larger  number  of  cases,  the  useful  qualities  of  the 
highly  improved  animals  of  the  farm  are  but  modifica- 
tions of  characters  which  were  already  present  in  the 
wild  forms.  The  function  of  milk  secretion  is  common 
to  all  mammals.  The  domestic  cow  is  valuable  because 
this  function  has,  through  selection  and  skillful  mating, 
been  gradually  improved.  The  quality  of  giving  a  small 
quantity  of  milk  found  in  the  wild  cow,  and  the  quality 
of  giving  a  large  quantity  of  milk  as  present  in  the  highly 
improved  dairy  cow,  are  not  contrasting  characters. 
The  one  is  but  a  modification  of  the  other  and  is  probably 
the  result  of  accumulated  fluctuating  variations  which 
have  been  preserved  by  methodical  selection.  It  will  be 
interesting  to  note  here  some  characters  among  animals 
which  have  already  been  found  to  conform  to  Mendel's 
law. 

138.  The  inheritance  of  polled  and  horned  character 
in  cattle.  —  Examples  of  Mendel's  law  are  much  more 
frequent  among  plants  than  animals.  The  complicated 
nature  of  animal  characteristics  has  made  it  difficult  to 
trace  the  workings  of  Mendel's  law  so  far  as  it  is  related 
to  many  animal  characters.  It  is  also  more  difficult 
to  find  contrasting  characters.  An  exception  to  the 
above  must  be  noted  in  the  case  of  the  horned  and  polled 
characters  in  cattle.  Whenever  a  pure  polled  animal 
is  mated  with  a  pure  horned  animal,  the  offspring  in  the 
first  generation  are  all  polled.  If  the  first  generation 


HEREDITY 


145 


offspring  are  interbred,  the  polled  and  horned  characters 
separate  in  the  second  generation  in  the  proportion  of 
25  per  cent  pure  polled,  50  per  cent  hybrid  polled,  and 
25  per  cent  pure  horned.  The  pure  polled  individuals, 


Horned 


HH        HH       HH 


1-  Polled  Hytr/d 

2-  Pure  Pa/fed 

3-  Pure  Horned 

FIG.  17.  —  Diagram  illustrating  mendelian  inheritance  as  exhibited 
in  the  transmission  of  polled  and  horned  characters  in  domestic  cattle. 

if  bred  to  others  of  their  own  kind,  produce  only  pure 
polled  offspring.  If  the  pure  horned  offspring  likewise 
are  mated  with  pure  horned  individuals,  their  offspring 
produce  pure  horned  offspring.  If  the  50  per  cent  hybrid 
polled  individuals  are  bred  to  other  hybrid  animals,  the 


146  THE   BREEDING   OF   ANIMALS 

result  is  the  same  as  in  the  second  generation.  The  off- 
spring will  be  25  per  cent  pure  polled,  25  per  cent  pure 
horned,  and  50  per  cent  hybrid  polled.  (See  Fig.  17.) 

This  principle  has  been  repeatedly  used  in  the  produc- 
tion of  polled  breeds  of  cattle.  The  only  practical  diffi- 
culty is  encountered  in  determining  which  of  the  second 
generation  are  pure  polled  and  which  are  hybrid  polled. 
This  difficulty  can  be  overcome  only  by  repeated  matings 
and  by  observation  of  the  offspring. 

139.  Theory  of  pure  lines.  —  The  practical  breeder 
of  animals  has  depended  almost  entirely  upon  methodical 
selection  for  the  improvement  of  domestic  animals.  It 
was  Darwin's  opinion  that  the  improvement  accom- 
plished in  the  desirable  qualities  of  animals  and  plants 
was  due  to  the  persistent  selection  of  desirable  continuous 
variations.  In  bringing  about  improvement,  therefore, 
the  breeder  only  required  keen  powers  of  observation 
to  detect  any  variations  in  a  standard  sort  which  were 
better  than  the  qualities  of  the  ancestors.  By  selecting 
these  varieties  and  continuing  this  process  for  many  gen- 
erations, highly  improved  sorts  were  ultimately  developed 
which  came  true  when  bred  together. 

In  the  practical  application  of  this  theory,  it  has  been 
frequently  discovered  that  the  limits  of  improvement 
through  selection  were  quickly  reached.  Apparently 
the  degree  of  improvement  could  not  be  carried  beyond 
a  certain  definite  point.  In  a  more  careful  analysis  of 
the  fundamental  basis  of  improvement  by  selection, 
Johanssen  l  has  demonstrated  that  very  many  of  the 
domestic  plants  are  not  possessed  of  single  characters 
only,  but  are  a  mixture.  The  selection  exercised  by 
man  in  such  cases  is  essentially  a  process  of  selecting  out 

1  Johanssen,  1909,  "Elemente  der  exakten  Erblichkeitslehre." 


HEREDITY  147 

the  most  desirable  strain  and  gradually  eliminating  the 
less  desirable.  This  is  the  pure  line  theory  and  is  now 
generally  accepted  as  applying  to  many  cases  of  improve- 
ment, especially  among  plants. 

An  acceptance  of  this  theory  recognizes  the  fact  that 
no  amount  of  selection  can  improve  a  pure  line  after  it 
has  been  separated  by  continuous  selection. 

An  hypothetical  example  of  pure  line  selection  among 
animals  might  be  imagined  in  the  case  of  the  wool  of  sheep. 
The  wool  produced  under  a  given  set  of  environmental 
conditions  in  a  flock  of  sheep  might  vary  from  eight  to 
twelve  pounds.  In  the  germ-cells  of  a  given  individual, 
we  may  assume  that  determiners  are  present  for  the  pro- 
duction of  eight,  ten  and  twelve  pounds.  In  breeding, 
these  varying  tendencies  may  be  separated.  It  is  con- 
ceivable that  some  of  the  offspring  may  have  inherited 
the  tendency  to  produce  twelve  pounds  of  wool,  while 
others  may  have  inherited  the  tendency  to  produce  eight 
pounds.  Through  many  generations  of  intelligent  selec- 
tion, the  flock-master  may  bring  about  a  more  or  less 
complete  separation  of  the  tendency  to  produce  twelve 
pounds  of  wool  and  may  thus  increase  the  average  pro- 
duction of  wool  from  his  flock.  The  application  of  this 
theory  to  animal-breeding  is  more  difficult  than  to  self- 
fertilizing  plants,  but  the  difficulties  are  partially  removed 
by  close  interbreeding. 

140.  Hallett's  wheat-breeding.  —  The  pure  line  method 
of  breeding  probably  explains  Hallett's  unusual  success 
in  the  improvement  of  wheat  in  Great  Britain.  However, 
it  must  be  said  that  Hallett  believed  that  improvement 
within  a  pure  line  of  selection  was  possible.  Hallett's 
method  may  be  best  described  by  using  his  own  words : 

"  A  grain  produces  a  '  stool '  consisting  of  many  ears. 


148  THE  BREEDING   OF  ANIMALS 

I  plant  the  grains  from  these  ears  in  such  a  manner  that 
each  ear  occupies  a  row  by  itself.  ...  At  harvest, 
after  the  most  careful  study  and  comparison  of  the  stools 
from  all  these  grains,  I  select  the  finest  one,  which  I 
accept  as  proof  that  its  parent  grain  was  the  best  of  all, 
under  the  peculiar  circumstances  of  that  season.  This 
process  is  repeated  annually,  starting  each  year  with 
the  proved  best  grain,  although  the  verification  of  this 
superiority  is  not  obtained  until  the  following  harvest. 

"  During  these  investigations  no  single  circumstance 
has  struck  me  as  more  forcibly  illustrating  the  necessity 
of  repeated  selection  than  the  fact,  that  of  the  grains  in 
the  same  ear  one  is  found  greatly  to  excel  the  others  in 
vital  power."  1 

Hallett's  experience  has  demonstrated,  first,  that 
great  improvement  may  be  secured  by  this  method  of 
selection.  Second,  he  advocated  the  "  ear  to  row " 
method.  Third,  it  is  probable  that  the  results  may  be 
satisfactorily  explained  by  Johanssen's  pure  line  theory. 

141.  The  presence  and  absence  hypothesis.  —  In 
Mendel's  conception  of  the  theory  of  dominant  and  reces- 
sive characters,  there  existed  a  definite  determiner  for 
both  the  dominant  and  recessive  characters.  Each  char- 
acter appeared  in  the  gametes  in  a  definite  form.  Later 
investigations  have  pointed  to  the  fact  that  the  dominant 
character  may  be  due  to  the  presence  of  a  specific  deter- 
miner, while  the  recessive  character  may  be  due  to  its 
absence.  This  conception  of  the  behavior  of  the  mende- 
lian  pair  of  characters  is  quite  different  from  Mendel's 
explanation. 

The  presence  and  absence  theory  has  contributed 
materially  to  the  science  of  genetics.  This  hypothesis 

1  Journal  of  the  Royal  Agricultural  Society,  vol.  22,  p.  371. 


HEREDITY  149 

has  made  it  possible  to  harmonize  many  of  the  observed 
phenomena  with  the  mendelian  principle.  It  has  also 
directed  the  attention  of  investigators  to  the  fundamental 
nature  of  the  characters  themselves.  Great  progress 
will  undoubtedly  be  made  in  the  future  in  the  direction 
of  a  more  thorough  study  and  consequently  better  under- 
standing of  the  real  nature  of  the  characters  of  both  plants 
and  animals. 

In  the  investigations  on  the  eye  color  of  man,  it  has 
been  found  that  the  dominant  character  is  due  to  a  brown 
pigment,  while  the  recessive  character  is  the  result  of  the 
absence  of  this  pigment.  Darbishire  1  has  clearly  indi- 
cated the  application  of  this  theory  in  the  case  of  the 
round  pea  and  the  wrinkled  pea.  The  quality  of  round- 
ness or  wrinkledness  as  found  in  the  garden  pea  is  due 
to  a  difference  in  the  amount  of  starch  in  the  pea.  In 
the  case  of  the  wrinkled  pea,  all  of  the  sugar  content  is 
converted  into  starch.  In  the  round  pea  a  much  more 
complete  transfer  of  sugar  to  starch  is  accomplished. 
The  inference  is  that  in  the  round  pea  there  is  present 
something  in  the  germ-cell  that  so  affects  the  physiological 
processes  in  the  cell  that  the  sugar  is  more  or  less  com- 
pletely turned  to  starch.  The  something  which  deter- 
mines this  change  of  sugar  to  starch  in  the  round  pea  is 
absent  from  the  germ-cell  in  the  wrinkled  pea.-  There- 
fore, we  have  two  varieties  of  pea  that  are  clearly  different* 
When  the  wrinkled  pea  and  the  round  pea  are  crossed, 
they  behave  in  accordance  with  the  mendelian  law.  It 
is  not  necessary  in  this  case  to  assume  that  the  determiner 
which  ultimately  results  in  a  round  pea  is  entirely  absent 
in  the  wrinkled  pea,  but  it  seems  to  be  entirely  correct 

1  Darbishire,  "Breeding  and  the  Mendelian  Discovery,"  p. 
127. 


150  THE   BREEDING   OF   ANIMALS 

to  assume  that  there  exists  an  insufficient  quantity  of 
this  substance  and  hence  an  incomplete  transposition  of 
sugar  to  starch  in  the  wrinkled  pea. 

It  is  not  at  present  possible  to  apply  the  presence  and 
absence  hypothesis  to  all  cases  of  apparent  mendelian 
inheritance.  That  it  applies  to  a  very  large  number  of 
characters  is  obvious,  but  as  pointed  out  by  Darbishire 
there  are  many  cases  which  cannot  at  the  present  time 
be  explained  on  this  theory,  and  in  fact  will  be  obstacles 
in  the  way  of  its  general  application.  Some  characters 
seem  to  be  dominant  in  one  class  of  plants  or  animals 
and  recessive  in  another.  The  polled  character  in  cattle 
is  unquestionably  dominant,  while  the  possession  of  horns 
is  a  recessive.  In  the  case  of  sheep  the  reverse  seems  to 
be  true.  The  white  color  of  pigs  is  dominant  to  black, 
but  the  black  color  of  sheep  is  dominant  to  white.1 

142.  The  theory  of  mutations.  —  It  is  clear  that  all 
improvements  in  the  domestic  animals  must  come  through 
variation.     If  the  offspring  was  always  an  exact  repro- 
duction of  the  parent,  improvement  would  be  impossible. 
But  how  have  the  improved  qualities  now  possessed  by 
our  domestic  animals  come  about?     Have  these  qualities 
come  through  a  gradual  and  continuous  series  of  changes, 
each  better  than  the  last,  or  have  they  come  through 
sudden  and  radical  variations  ?    A  study  of  the  ancestral 
history  of  both  plants  and  animals  gives  clear  evidence 
that  new  types  have  originated  by  both  kinds  of  variation. 

143.  Two   important  classes   of  variation.  —  Darwin 
recognized  these  two  distinct  types  of  variation,   but 
believed  that  the  most  important  changes  in  organic 
beings  were  due  to  small  but  gradual  and  continuous 
variations  in  a  given  direction.     In  his  earlier  writings 

^unnett,  "MeDdelism,"  p.  29. 


•  HEREDITY  151 

Darwin  emphasized  the  great  importance  of  continuous 
or  fluctuating  variations.  He  says,  "  It  may  be  doubted 
whether  sudden  and  considerable  deviations  of  structure 
such  as  we  occasionally  see  in  our  domestic  productions, 
more  especially  with  plants,  are  ever  permanently  prop- 
agated in  a  state  of  nature.  Almost  every  part  of  every 
organic  being  is  so  beautifully  related  to  its  complex 
conditions  of  life  that  it  seems  as  improbable  that  any 
part  should  have  been  suddenly  produced  perfect,  as 
that  a  complex  machine  should  have  been  invented  by 
man  in  a  perfect  state." 

Sudden  variations  were  called  by  Darwin  discontinuous. 
Variations  frequently  occur  which  vary  widely  from 
the  parent  form.  Examples  of  this  kind  of  variation 
are  common  in  both  plants  and  animals.  The  normal 
fruit  of  a  peach  tree  is  a  typical  peach  having  a  rough 
skin  and  a  flavor  and  color  peculiar  to  the  peach. 
Branches  of  peach  trees,  however,  sometimes  produce  a 
fruit  known  as  a  nectarine.  This  is  smooth,  smaller 
than  the  peach,  and  possessed  of  a  color,  flavor  and  physical 
consistence  markedly  different  from  the  normal  fruit  of 
the  peach. 

Among  animals  mutations  frequently  occur.  Varia- 
tions in  the  number  of  digits  have  been  recorded  by  a 
large  number  of  investigators.  Huxley  describes  the 
case  of  a  man  born  with  six  fingers  on  each  hand  and  six 
toes  on  each  foot.  Four  children  were  born  to  this  man. 
The  first,  a  male  child,  was  born  with  six  fingers  on  each 
hand  and  six  toes  on  each  foot.  The  second  child,  a 
boy,  had  five  fingers  and  five  toes,  but  one  toe  was  de- 
formed. The  third  child,  also  a  boy,  had  five  perfect 
fingers  and  toes,  but  the  fourth  child,  a  girl,  although 
having  the  normal  number  of  digits,  had  deformed  thumbs. 


152  THE  BREEDING  OF  ANIMALS 

The  mutation  appearing  in  the  father  was  not  only  a 
radical  variation,  but  there  existed  a  strong  tendency  to 
transmit  the  abnormality.  The  strength  with  which 
mutations  are  transmitted  is  still  further  indicated  by 
the  later  history  of  the  sons  and  daughters  of  the  father. 
"  Salvator  had  four  children  —  they  were  two  boys,  a 
girl,  and  another  boy  —  the  first  two  boys  and  the  girl 
were  six-fingered  and  six-toed  like  their  grandfather; 
the  fourth  boy  had  only  five  fingers  and  toes. 

"  George  had  only  four  children ;  there  were  two  girls 
with  six  fingers  and  six  toes ;  there  was  one  girl  with  six 
fingers  and  five  toes  on  the  right  side,  and  five  fingers  and 
five  toes  on  the  left  side,  so  that  she  was  half-and-half. 
The  third,  Andre,  you  will  recollect,  was  perfectly  well 
formed,  and  he  had  many  children  whose  hands  and  feet 
were  all  regularly  developed. 

"  Marie,  the  last,  who  of  course  married  a  man  who 
had  only  five  fingers,  had  four  children :  the  first,  a  boy, 
was  born  with  six  toes,  but  the  other  three  were  normal."  1 

Some  marked  variations  among  the  domestic  animals 
which  have  been  recorded  from  time  to  time  and  which 
are  probably  true  mutations  may  be  mentioned.  The 
normal  foot  of  domestic  swine  is  cleft,  but  solid-hoofed 
hogs  are  common,  and  this  mutation  is  strongly  trans- 
mitted. The  breed  of  swine  known  as  "  mule-footed 
hogs  "  is  an  example.  Horned  sheep  normally  possess- 
ing two  horns  are  sometimes  born  with  four  horns.  The 
offspring  of  horned  cattle  are  sometimes  born  without 
horns,  and  this  variation  is  strongly  transmitted. 

To  Hugo  De  Vries  of  Amsterdam  we  owe  our  present 
definite  notions  regarding  the  theory  of  mutations.  While 
such  variations  were  recognized  by  Darwin  and  other 

1  Huxley,  quoted  in  Miles'  "Stock  Breeding,"  p.  79. 


HEREDITY  153 

investigators,  it  remained  for  De  Vries  to  demonstrate 
by  scientific  investigation  the  important  role  played  by 
mutations  in  the  evolution  of  plants  and  animals.  This 
theory  undertakes  to  explain  the  origin  of  species  by  sud- 
den marked  variations  rather  than  by  continuous  or 
fluctuating  variations.  De  Vries'  experiments  were  suc- 
cessful not  only  in  demonstrating  clearly  the  remarkable 
tendency  of  certain  species  to  vary  abruptly,  but  of  even 
more  significance  was  his  demonstration  of  the  fact  that 
such  variations  were  as  surely  transmitted  as  were  the 
regular  or  normal  characters  of  the  species. 

It  is  true,  mutations  must  not  be  confounded  with 
the  appearance  of  freaks  or  monstrosities  among  plants 
and  animals.  Often  through  arrested  development  or 
accidental  injury  during  the  embryonic  existence  of  ani- 
mals, certain  characteristics  may  become  so  modified 
that  they  appear  in  the  form  of  new  characters.  Such 
freaks  are  not  transmitted  and  are  not  therefore  muta- 
tions. The  term  mutations  is  used  only  to  designate 
those  variations  which  are  heritable. 

144.  Kinds  of  mutations.  —  Mutations  may  be  addi- 
tions or  improvements  to  the  life  of  organic  beings,  or 
they  may  result  in  diminishing  the  ability  of  an  animal 
or  plant  to  live  and  thrive  in  an  ordinary  environment. 
De  Vries  has  therefore  suggested  a  classification  of  muta- 
tions as  progressive,  regressive  and  degressive. 

Progressive  mutations  are  those  which  have  contrib- 
uted something  entirely  new.  It  is  in  reality  an  addi- 
tional character.  Attention  has  already  been  called 
to  cases  of  variation  in  which  the  offspring  is  provided 
with  extra  fingers  or  toes.  An  example  of  this  form  of 
mutation  is  described  by  Alexander  Graham  Bell  in  the 
case  of  multi-nippled  sheep. 


154  THE   BREEDING   OF   ANIMALS 

In  regressive  mutations  the  animal  actually  loses 
some  hereditary  character  that  it  has  formerly  possessed. 
An  animal  may  be  born  with  less  than  the  normal  number 
of  digits,  and  this  may  be  transmitted  to  offspring.  The 
so-called  tailless  breed  of  cats  is  probably  descended 
from  an  individual  born  without  a  tail.  A  polled  animal, 
the  offspring  of  horned  parents,  would  also  be  an  example 
of  regressive  mutation. 

The  term  degressive  has  been  applied  to  such  varia- 
tions as  have  existed  in  the  previous  ancestral  history  of 
the  animal  or  plant.  When  such  variations  reappear 
after  many  generations,  they  are  known  as  degressive 
mutations. 

145.  Importance  of  the  mutation  theory.  —  The  im- 
portance of  the  mutation  theory  to  the  animal-breeder 
lies  in  the  fact  that  many  of  the  most  important  and  useful 
qualities  present  in  the  domestic  animals  have  probably 
arisen  through  sudden  variations  or  mutations.  Such 
mutations  are  likely  to  occur  at  any  time.  It  is  indeed 
probable  that  such  mutations  do  occur  frequently.  The 
intelligent  breeder  who  understands  the  laws  of  evolution 
will  clearly  recognize  the  importance  of  such  mutations. 
The  fact  that  they  are  certainly  transmitted  by  heredity 
has  given  to  the  breeder  a  most  important  method  in 
the  permanent  improvement  of  the  domestic  animals. 
It  is,  of  course,  quite  as  true  that  mutations  may  be 
degressive  and  thus  actually  be  of  less  value  than  the  par- 
ent forms.  Certain  breeds  are  probably  more  variable 
than  others,  and  this  fact  may  be  both  an  advantage  and 
a  disadvantage.  It  is  a  desirable  condition  in  that  mu- 
tations may  occur  and  some  of  these  may  be  improve- 
ments over  the  parent  species.  Such  a  tendency  to  vary 
may  be  a  disadvantage  in  that  the  variations  may  some- 


HEREDITY  155 

times  be  in  the  direction  of  less  valuable  characters. 
Eventually  no  breed  of  animals  can  be  most  useful  until 
the  desirable  characters  are  firmly  fixed  and  reasonably 
certain  to  be  transmitted  by  inheritance. 

146.  Mono-hybrids  and  di-hybrids.  —  In  all  of  the 
examples  so  far  used  to  illustrate  the  principles  of  segrega- 
tion and  dominance  as  developed  by  Mendel,  only  such 
simple  unit  characters  have  been  employed  as  indicate 
clearly  the  law  of  Mendel.  Such  simple  contrasting 
characters  are  known  as  mono-hybrid.  It  is  easy  to 
demonstrate  the  mendelian  hypothesis  in  the  case  of 
mono-hybrids. 

But  among  domestic  animals  the  qualities  which  have 
made  organic  beings  useful  to  man  are  in  most  part  a 
combination  of  two  or  more  unit  characters.  In  such 
cases  it  is  far  more  difficult  to  use  the  mendelian  formula. 
Mendel  himself  determined  the  probable  application  of 
the  principle  to  cases  where  two  different  unit  characters 
were  present.  He  crossed  the  wrinkled  green  peas  with 
smooth  yellow  peas.  Manifestly,  the  number  of  com- 
binations of  characters  was  greater  than  when  mono- 
hybrids  were  examined.  The  proportion  of  3  plus  1  is 
the  universal  result  in  the  FI  generation  where  single  unit 
characters  are  involved.  Mendel  found  in  the  case  of 
combinations  of  two  unit  characters  that  the  mathemat- 
ical statement  (3  plus  I)2  (16)  represented  the  true 
result.  There  would  appear  sixteen  possible  zygotes  as 
a  result  of  crossing  individuals  containing  two  unit 
characters  in  each  of  the  parents.  In  the  offspring  result- 
ing from  such  crosses  the  characters  would  be  combined 
in  such  a  manner  as  to  produce  sixteen  kinds  of  indi- 
viduals. 

It  is  apparent  that  if  the  number  of  combinations  of 


156  THE   BREEDING   OF  ANIMALS 

unit  characters  increases,  the  number  of  possible  different 
individuals  produced  by  crossing  similarly  increases. 
In  the  case  of  tri-hybrids  in  which  three  characters  com- 
bine, the  number  of  different  individuals  or  zygotes  pro- 
duced would  be  represented  by  (3  plus  I)4.  For  the 
purposes  of  the  practical  breeder,  therefore,  little  progress 
is  possible  except  in  cases  where  one  or  two  characters 
only  are  involved.  In  those  cases  in  which  the  characters 
involved  are  made  of  a  combination  of  many  units  it  is 
first  necessary  that  the  important  unit  characters  be 
separated  by  long-continued  breeding;  in  other  words, 
until  it  becomes  homozygous.  By  such  methods,  it  is 
possible  to  obtain  recombinations,  and  from  the  point 
of  view  of  the  practical  breeder,  entirely  new  characters. 
The  mendelian  principle  may,  therefore,  in  this  way  be- 
come a  powerful  instrument  in  the  future  improvement  of 
domestic  plants  and  animals. 


CHAPTER  VIII 
INHERITANCE  OF  ACQUIRED  CHARACTERS 

THE  normal  characteristics  of  all  organic  beings  may 
be  greatly  modified  by  external  conditions  acting  con- 
tinuously upon  the  organism  for  a  longer  or  shorter 
period  of  time.  Such  modifications  may  be  of  so  marked 
a  character  as  to  cause  an  apparent  departure  from  the 
average  or  normal  characteristics  of  the  race.  Through 
accident,  disease  or  by  design,  the  animal  or  plant  may 
become  permanently  mutilated.  The  modifications  which 
result  from  the  causes  mentioned  may  make  the  domestic 
animal  or  plant  more  useful  to  man  than  the  normal 
organism ;  the  changes  may  in  fact  be  real  improvements, 
and  as  such  it  would  be  very  desirable  to  perpetuate 
them  by  heredity.  Thus  the  breeder  of  domestic  ani- 
mals, having  accurately  observed  the  general  fact  of 
inheritance  of  the  normal  characters,  has  reasoned  that 
such  remarkable  changes  as  those  often  resulting  from 
use  or  disuse,  favorable  environment  or  mutilations  must 
be  transmitted  with  equal  force. 

147.  Belief  in  transmission  of  acquired  characters.  — 
The  literature  of  the  ancients  indicates  that  the  philos- 
ophers of  that  period  believed  in  the  inheritance  of 
acquired  characters.  Aristotle  mentions  the  transmission 
of  the  exact  shape  of  a  cautery  mark.  At  a  much  later 
period  Lamarck  elaborated  his  theory  of  variation  and 
selection  which  took  for  granted  that  all  modifications 

157 


158  THE   BREEDING   OF  ANIMALS 

resulting  from  use  and  disuse  and  the  effects  of  environ- 
ment were  transmitted  by  heredity.1 

Among  those  who  have  failed  to  find  satisfactory 
evidence  of  the  inheritance  of  modifications  must  be 
mentioned  Kant,  Blumenbach,  and  later  Gal  ton,  Weis- 
mann,  Ray  Lankester  and  practically  all  the  leading 
biologists  of  modern  times. 

148.  Practical  breeders  believe  in  transmission  of 
acquired  characters.  —  There  is  a  widespread  belief 
among  the  breeders  of  domestic  animals  that  acquired 
characters  are  inherited.  To  the  practical  breeder  of 
dogs  who  has  observed  the  sensitive  reaction  of  the  fox 
hound  to  the  scent  of  the  fox,  or  the  alertness  of  the  setter 
or  pointer  in  the  presence  of  a  fresh  bird  track,  it  is  diffi- 
cult to  find  a  satisfactory  explanation  for  existing  facts 
without  assuming  that  the  results  of  the  training  of  a 
dog  to  some  extent  must  be  transmitted.  Extreme  speed 
in  running  and  trotting  horses  is  the  result  of  training 
and  exercise.  The  offspring  of  parents  who  have  acquired 
extreme  speed  through  training  and  exercise  are  more  apt 
to  possess  the  ability  to  acquire  similar  extreme  speed 
than  the  offspring  of  parents  who  have  not  been  trained. 
The  practical  breeder  concludes,  therefore,  that  the  ac- 
quired speed  must  be  transmitted. 

There  are  many  breeders  of  beef  cattle  who  firmly 
believe  that  by  maintaining  the  breeding  animals  in  high 
condition,  the  calves  will  have  a  more  pronounced  devel- 
opment of  those  characters  which  are  recognized  as 
belonging  to  the  beef  type  than  will  the  calves  of  parents 
which  are  maintained  on  a  low  plane  of  nutrition. 

The  breeder  is  an  accurate  observer,  and  there  can  be 
no  question  that  his  facts  are  generally  correct  in  this 
1  Thomson,  "  Heredity,"  p.  170. 


i 


'QUIRED   CHARACTERS     159 


!l  '"          "  '-.i-G'1  '  '  > 


t  ID< 


160  THE  BREEDING  OF  ANIMALS 

The  most  notable  examples  of  acquired  development 
are  to  be  found  in  the  human  family.  Through  the  life- 
time of  a  man  the  mental  and  physical  qualities  may  be 
greatly  modified.  An  individual  may  acquire  great 
mental  power.  Such  acquirement  may  have  been 
achieved  under  very  great  difficulties.  The  particular 
kind  of  mental  efficiency  represented  by  the  develop- 
ment of  such  an  individual  may  be  an  exceedingly  desir- 
able characteristic  of  the  greatest  value  to  the  human 
race.  Its  transmission  by  heredity  would  be  desirable 
for  the  good  of  the  race.  Can  such  acquired  characters 
or  habits  be  transmitted?  The  answer  to  this  question 
is  important  to  the  development  of  the  human  race.  It 
is  likewise  of  the  greatest  economic  importance  to  the 
breeder  of  domestic  animals.  In  the  domestic  animals 
the  highly  artificial  characters  possessed  by  the  improved 
forms  of  cattle,  horses,  sheep  and  swine  are  very  largely 
due  to  the  development  or  good  handling  to  which  these 
animals  have  been  subjected.  If  the  results  of  the 
high  degree  of  development  of  one  generation  are  to 
fundamentally  influence  the  characters  of  the  next,  then 
a  new  significance  will  be  given  to  the  effects  of  environ- 
ment. 

150.  What  are  acquired  characters?  —  The  use  of 
the  term  acquired  characters  to  indicate  entirely  different 
facts  has  given  rise  to  some  confusion  in  the  consideration 
of  this  subject.  In  one  sense  no  character  is  ever  trans- 
mitted. Only  the  determiners  which  give  direction  to 
the  developing  characters  of  the  animal  or  plant  are 
actually  inherited.  The  characters  themselves  develop 
out  of  and  are  determined  by  the  fundamental  constit- 
uents of  the  germ  substance.  Thus  the  appearance  of 
the  secondary  sexual  characters  of  the  male  at  puberty 


INHERITANCE  OF  ACQUIRED   CHARACTERS     161 

are  not  acquired  characters  in  the  biological  sense.  Ac- 
quired characters  are  modifications  of  the  somatic  cells 
which  are  induced  by  environment,  use  or  disuse,  acci- 
dents or  any  other  influences  acting  upon  the  body-cells 
in  such  a  way  as  to  change  their  normal  development. 
According  to  Weismann,  if  the  modifications  are  the  result 
of  the  presence  of  determiners  in  the  germ-plasm,  then 
they  are  not  properly  designated  as  acquired  characters. 

151.  Somatoplasm  and  germ-plasm.  —  From  the  view- 
point of  the  biologist,  all  organic  beings  which  reproduce 
sexually  are  differentiated  into  two  very  clearly  defined 
groups  of  cells :  the  somatic  group,  which  includes  all 
the  cells  concerned  in  the  processes  of  nutrition,  includ- 
ing digestion,  absorption  and  assimilation;  the  nerve 
cells  and  all  other  cells  involved  in  the  physiological 
activities  of  the  organized  being,  except  the  reproductive 
cells. 

Distinct  and  apart  from  the  soma-  or  body-cells  are 
the  germ-cells,  the  function  of  which  is  to  provide  for 
the  reproduction  of  the  species.  Weismann  was  the 
first  to  point  out  clearly  the  very  sharp  division  between 
the  fundamental  organization  and  function  of  these  two 
groups.  The  somatoplasm  has  its  origin  in  the  germ- 
plasm,  and  the  direction  of  its  development  is  controlled 
by  the  determiners  in  the  germ-plasm,  but  the  germ- 
plasm  is  not  influenced  in  any  fundamental  way  by  the 
somatoplasm.  The  soma  is  to  be  regarded  in  the  nature 
of  a  habitat  for  the  successful  activities  of  the  germ-cells. 
In  a  sense,  the  somatoplasm  has  no  more  influence  upon 
the  developing  germ-cells  harbored  within  the  soma  than 
does  the  soil  upon  the  trees  which  may  develop  from 
the  seeds  planted  on  its  surface. 

The  germ-plasm  is  continuous.     It  is  a  part  of  the 

M 


162  THE  BREEDING  OF  ANIMALS 

germ-plasm  of  the  preceding  generation.  If  this  dis- 
tinction and  differentiation  is  kept  clearly  in  mind,  it 
will  help  materially  in  the  discussion  of  the  inheritance 
of  acquired  characters.  If  we  accept  Weismann's  def- 
inition of  acquired  characters,  that  they  are  somatic 
modifications  which  do  not  have  their  origin  in  the  germ- 
plasm,  we  have  to  discuss  only  such  somatic  modifications 
as  may  be  acquired  by  the  animal  during  its  lifetime. 

152.  Examples  of  acquired  characters.  —  Among  the 
common  causes  of  the  changes  in  the  soma  must  be 
grouped  environment,  including  food  and  climate;    use 
and  disuse  of  parts;    disease  and  accidents.     Each  of 
these  acting  separately  or  all  of  them  acting  together  may 
cause  profound  changes  in  the  external  form  and  develop- 
ment of  plants  and  animals. 

153.  Food  supply.  —  Perhaps  no  other  single  environ- 
mental influence  is  responsible  for  such  profound  changes 
in  the  external  form  of  plants  and  animals  as  the  food 
supply.    The  Kerry  cattle  of  Ireland  are  a  diminutive 
race  of  cattle  which  have  been  long  subjected  to  condi- 
tions of  scant  supply  of  innutritious  food.    Their  size 
and  hardy  character  must  be  regarded  as  a  more  or  less 
successful  adaptation  to  their  environment.     When  young 
calves  of  the  Kerry  breed  are  surrounded  with  conditions 
in  which  they  are  supplied  with  a  generous  and  nutri- 
tious food,  they  increase  in  size  and  come  to  maturity 
at  an  earlier  age.1 

The  Shetland  pony  in  the  barren  islands  of  Shetland, 
gathering  a  scant  subsistence  from  the  inferior  grasses 
and  forage  plants,  develops  into  one  of  the  most  diminu- 
tive races  of  horses  known  to  man.  The  same  race  of 
horses  transplanted  to  the  fertile  regions  of  Great  Britain 
1  Miles,  "Principles  of  Stock  Breeding,"  p.  100. 


@ 


PLATE  VII.  —  Upper.  Ration  not  restricted.  Fed  for  rapid  growth 
and  development  from  age  90  days.  Age  716  days,  weight  1401  pounds. 
Lower.  Ration  greatly  restricted.  Age  777  days,  weight  512  pounds, 
height  121  cm. 


PLATE  VIII.  —  Upper.  Ration  not  restricted.  Fed  for  rapid  growth 
and  development  from  age  90  days.  Age  336  days,  weight  875  pounds. 
Lower.  Ration  partially  restricted.  Fed  for  normal  but  moderate 
growth  and  development.  Age  780  days,  weight  813  pounds,  height 
128  cm.  Compare  with  Plate  VII. 


INHERITANCE  OF  ACQUIRED   CHARACTERS     163 

or  America  increases  in  size  as  the  result  of  a  better  food 
supply. 

Woltereck,  by  changing  the  food  supply  only,  in  hyalo- 
daphnia,  succeeded  in  changing  the  percentage  of  the 
height  of  the  head  to  that  of  the  body  from  40  to  over  90. 

The  remarkable  influence  of  the  amount  of  food  supplied 
to  an  animal  during  its  development  in  modifying  the 
somatic  cells  and  changing  the  external  form  of  animals, 
is  well  illustrated  by  the  unpublished  results  of  an  experi- 
ment conducted  at  the  Missouri  Experiment  Station.1 
In  this  investigation,  the  animals  were  maintained  for 
long  periods  upon  different  planes  of  nutrition. 

For  the  purpose  of  this  investigation  the  animals  were 
divided  into  three  groups.  Group  one  (see  Plates  VII, 
VIII  and  IX)  was  supplied  with  a  generous  ration  cal- 
culated to  furnish  to  the  animal  all  the  nutrients  it 
could  utilize,  and  produce  the  maximum  growth  and 
development,  including  the  laying  on  of  fat.  The  treat- 
ment given  to  group  one  resulted  not  only  in  very 
rapid  growth  and  development,  but  as  the  excessive 
feeding  was  long  continued,  the  animals  laid  on  unusual 
and  excessive  amounts  of  fat. 

The  ration  supplied  to  group  two  (see  Plate  VIII, 
lower)  was  intended  to  provide  such  a  quantity  of  food 
as  was  sufficient  to  produce  strong,  healthy  growth  and 
development,  but  insufficient  for  laying  on  any  consider- 
able amount  of  fat.  This  ration  resulted  in  normal, 
healthy  growth,  but  the  food  supplied  was  constantly 
below  the  desires  and  appetites  of  the  animals.  There 
was  no  time  during  the  experiment  at  which  the  animals 
would  not  have  consumed  more  food. 

1  Waters  and  Trowbridge,  Unpublished  Data  from  the  Mis- 
souri Experiment  Station. 


164  THE   BREEDING  OF  ANIMALS 

Group  three  (Plate  VII,  lower)  was  limited  markedly  in 
the  amount  of  food  which  the  animals  were  permitted  to 
consume.  The  scant  ration  given  to  group  three  did  not 
prevent  the  animals  from  growing,  but  it  did  prevent  the 
animals  from  making  a  normal  growth,  and  prevented  the 
normal  deposition  of  fat  within  the  body  tissues,  which 
seems  to  be  a  favorable  factor  in  inducing  healthy  growth 
and  development. 

The  illustrations  represent  typical  animals  in  the  three 
groups.  These  illustrations  give  a  general  impression 
of  the  changes  in  body  form  which  are  readily  apparent 
to  the  eye,  resulting  from  the  methods  of  treatment  of 
these  various  groups. 

154.  Influence  of  the  amount  of  food  on  body  weight.  — 
A  record  of  the  changes  in  the  body  weight  of  an  animal 
is  not  the  most  accurate  measure  of  the  influence  of  any 
environmental  factor,  but  it  is  sometimes  very  useful, 
and  often  the  best  measure  available.  In  this  experi- 
ment, animal  501,  which  was  fed  for  forty-seven  months 
on  a  full  ration,  attained  in  that  time  a  total  weight  of 
1965  pounds.  Animal  512,  fed  a  medium  ration  for 
forty-eight  months,  attained  a  weight  during  that  period 
of  1224  pounds.  Animal  500,  belonging  to  the  low-fed 
group,  weighed,  at  the  end  of  the  forty-eight  months'  feed- 
ing, 1042  pounds.  The  differences  observed  in  these 
animals  must  be  due  entirely  to  the  differences  in  the 
amount  of  food  supplied,  as  they  were  subjected  to  iden- 
tical conditions  in  all  other  respects.  The  experiment 
would  have  been  still  more  valuable  if  the  animals  in  the 
three  groups  had  been  fed  on  the  different  rations  from 
birth.  As  a  matter  of  fact,  the  animals  in  all  the  groups 
were  generously  fed  during  the  first  five  months  of  their 
lives. 


PLATE  IX.  —  Upper.  Steer  527  weighing  200  pounds  at  age  120 
days.  Fed  maximum  ration  for  rapid  growth  and  development  from 
age  90  days.  Lower.  Same,  weighing  1453  pounds  at  age  27  months ; 
rations  not  restricted. 


INHERITANCE   OF  ACQUIRED   CHARACTERS     165 

155.  Food  supply  and  body  changes.  —  All  the  evi- 
dence available  points  to  the  fact  that  the  domestic  ani- 
mals have  inherited  not  only  a  tendency  to  reach  a  cer- 
tain size  and  form,  Hut  that  they  have  inherited  a  strong 
tendency  to  attain  a  given  size  at  a  certain  age.    Thus, 
in    these    investigations    at    the    Missouri    Experiment 
Station,  there  is  evidence  to  show  that  the  animal  organ- 
ism makes  desperate  efforts  to  grow,  even  when  the  food 
supply  is  greatly  limited.     In  one  case  a  calf  nine-and- 
one-half  months  old  was  fed   a  limited   ration  which 
resulted  in  a  loss  of  weight  amounting  to  82  pounds  in 
six  months.     During    the  same  period  this  animal  in- 
creased 8.1  per  cent  in  height  and  14  J  per  cent  in  length 
of  head.1 

156.  Influence  of  limited  food  supply  from  birth.  — 
The  amount  of  food  supplied  to  a  growing  animal  in  a 
large  measure  determines  not  only  its  ultimate  develop- 
ment, but  the  rate  at  which  the  animals  grow.     In  another 
investigation  at  the  Missouri  Experiment  Station,2  three 
animals  were  fed  a  full  ration,  a  medium  ration  and  a 
scant  ration,  respectively.    Animal  number  527  (Plate  VII, 
upper)  given  a  full  ration,  increased  in  weight  rapidly,  and 
at  the  end  of  789  days  weighed  1453  pounds.     Animal  559 
(Plate  VIII,  lower),  given  a  medium  ration  intended  to 
produce  a  normal  growth,  but  not  a  fattening  ration,  at 
the  end  of  780  days  weighed  813  pounds.     Animal  551 
(Plate  VII,  lower) ,  given  a  scant  ration,  weighed  at  777  days 
512  pounds.     It  is,  of  course,  possible  that  in  these  experi- 
ments the  differences  in  body  weight  may  be  due  to  the 

1  Waters,  Proceedings  of  the  Society  for  the  Promotion  of  Agri- 
cultural Science,  1908. 

2  Waters  and  P.  F.  Trowbridge,  Unpublished  Data  of   the 
Missouri  Experiment  Station. 


166  THE   BREEDING   OF   ANIMALS 

amount  of  fat  deposited  in  the  tissues  rather  than  to  differ- 
ences in  the  development  of  the  skeleton  and  muscular  tis- 
sues. The  very  great  differences  in  weight  noted  are  of  the 
greatest  significance  if  they  represent  differences  in  the 
fundamental  skeletal  and  muscular  tissues  of  the  body. 
If  they  represent  alone  differences  in  the  amount  of  fat, 
they  are  not  so  significant.  The  height  of  each  animal 
as  observed  seems  to  indicate  clearly  that  not  only  is 
the  amount  of  fat  deposited  in  the  tissues  directly 
determined  by  the  amount  of  food  available,  but  the 
skeletal  growth  also  is  profoundly  influenced  by  the  food 
supply. 

There  can  be  no  question  but  that  limiting  the  amount 
of  food  supplied  to  young  animals  has  a  profound  influ- 
ence upon  the  rate  of  growth  as  well  as  its  ultimate  size. 
This  influence  is  to  be  found  in  smaller  skeleton,  probably 
arrested  development  of  the  muscular  tissues,  and  a  much 
smaller  percentage  of  fat. 

157.  Telegony.  —  There  was  a  time  when  eminent 
biologists  and  practical  breeders  firmly  believed  that  the 
influence  of  the  sire  was  not  confined  to  his  immediate 
offspring  but  the  mother  herself  was  in  some  manner  so 
impressed  with  the  characters  of  the  sire  that  her  subse- 
quent progeny  sired  by  entirely  different  males  might 
take  on  the  characters  of  the  former  sire.  "  The  act  of 
fecundation  is  not  an  act  which  is  limited  in  its  effect," 
says  Agassiz,1  "  but  that  it  is  an  act  which  affects  the 
whole  system,  the  sexual  system  especially;  and  in  the 
sexual  system  the  ovary  to  be  impregnated  hereafter 
is  so  modified  by  the  first  act  that  later  impregnations 
do  not  efface  that  first  impression."  Darwin  supported 
his  belief  in  telegony  by  citing  many  cases  among  plants 

1  Massachusetts  State  Board  of  Agriculture,  1863,  p.  56. 


INHERITANCE   OF  ACQUIRED   CHARACTERS     167 

of  "  direct  action  of  the  male  element  on  the  mother 
form."  He  remarks  further  that  "  the  male  element 
not  only  affects,  in  accordance  with  its  proper  function, 
the  germ,  but  the  surrounding  tissues  of  the  mother 
plant." 

Spencer  likewise  admitted  the  probability  of  the  pas- 
sage of  the  germ-plasm  from  the  growing  embryo  into  the 
maternal  tissues  and  thus  to  the  germ-cells.  Weismann 
held  that  if  any  such  influence  in  reality  existed,  it  could 
be  explained  only  on  the  theory  that  some  of  the  sperm- 
cells  of  the  male  penetrated  to  the  undeveloped  ova  and 
there  accomplished  a  partial  impregnation.  Some  prac- 
tical .breeders,  of  horses  and  dogs  particularly,  were  so 
thoroughly  impressed  with  the  possibility  of  such  an 
influence  that  they  would  not  buy  a  highly  bred  animal 
that  had  borne  offspring  to  another  breed,  believing  that 
such  a  female  could  not  be  trusted  to  breed  true.  Some 
farmers  in  the  mule-breeding  districts  have  reported 
that  horse  foals  from  mares  which  had  previously  pro- 
duced mules,  sometimes  possessed  "  mulish  characters." 
These  characters  which  are  commonly  possessed  by  the 
hybrid  appearing  thus  in  pure  horse  foals  were  supposed 
to  have  come  about  through  the  influence  of  the  jack  on 
the  mother  at  some  previous  mating. 

158.  The  Lord  Morton  mare.  —  One  of  the  most 
striking  cases  of  supposed  infection  was  reported  to  the 
Royal  Society  1  by  Lord  Morton  in  1820. 

The  essential  facts  are  discussed  by  Darwin.2  In  the 
year  1815  Lord  Morton  bred  a  seven-eighths  Arabian 
mare  of  chestnut  color  to  a  quagga.  The  resulting 

1  Philosophical  Transactions,  1821,  p.  21. 

2  Darwin,    "Animals    and    Plants    under    Domestication," 
vol.  I. 


168  THE   BREEDING   OF  ANIMALS 

offspring  was  a  true  hybrid  having  the  same  color 
and  in  other  characters  resembling  the  sire.  Later  in 
1817,  1818  and  1821  the  same  mare  was  bred  to  a  black 
Arabian  stallion  and  from  each  mating  produced  a  healthy 
foal  which  in  every  case  was  marked  with  stripes  like 
the  quagga  sire,  and  resembling  the  sire  also  in  the  char- 
acter of  the  mane.  Lord  Morton,  in  describing  the 
particular  resemblances  of  these  foals,  says :  "  Both  in 
their  color  and  in  the  hair  of  their  manes  they  have  a 
striking  resemblance  to  the  quagga.  Their  color  is 
very  marked,  more  or  less  like  the  quagga  in  a  darker 
tint.  Both  are  distinguished  by  the  dark  line  along  the 
ridge  of  the  back,  the  dark  stripes  across  the  forehead 
and  the  dark  bars  across  the  back  part  of  the  legs."  1 
The  existence  of  stripes  or  bars  on  young  foals  is  not 
uncommon,  and  their  presence  on  the  offspring  of  the 
Lord  Morton  mare  may  be  explained  on  other  grounds 
than  the  assumption  that  they  were  caused  by  the  influ- 
ence of  a  previous  impregnation  of  the  Arabian  mare  by 
the  quagga  sire. 

159.  The  Penycuik  experiments.  —  The  possibility  of 
tracing  to  some  other  source  the  real  or  fancied  resem- 
blances of  the  Arabian  foals  to  the  quagga  sire  of  a  pre- 
vious mating,  led  Cossar  Ewart  to  make  a  thorough  inves- 
tigation of  the  so-called  infection  theory.  At  Penycuik 
in  1895  Ewart  repeated  as  closely  as  possible  the  breed- 
ing experiment  of  Lord  Morton.  In  these  experiments 
thirteen  mares  of  varied  colors  and  breeds  produced  a 
total  of  sixteen  foals  to  a  Burchell  zebra.  The  same  mares 
later  produced  twenty-two  foals  by  Arab,  Thoroughbred 
and  Highland  stallions.  Ewart,  in  describing  a  typical 

1  Ewart,  Bureau  of  Animal  Industry  Report,  1910,  U.  S. 
Dept.  of  Agr. 


INHERITANCE  OF  ACQUIRED   CHARACTERS     169 

result,  says : 1  "  The  first  hybrid  was  born  August  12, 
1896,  the  dam  being  Mulatto,  a  black  Highland  pony 
lent  by  Lord  Arthur  Cecil." 

"  In  1897  Mulatto  had  a  foal  to  Benazrek,  a  gray  Arab 
stallion.  As  this  subsequent  foal  of  Mulatto  was  indis- 
tinctly striped,  I  was  at  first  inclined  to  believe  she  had 
been  infected  by  her  first  sire,  the  zebra  Matopo;  but 
when  more  richly  striped  pure-bred  foals  were  obtained 
later  by  Benazrek  out  of  Highland  mares  which  had  never 
even  seen  a  zebra,  it  became  evident  that  Mulatto  af- 
forded no  evidence  in  support  of  the  infection  doctrine. 

"  Lord  Morton's  quagga  counted  for  so  little  in  the 
hybrid  out  of  the  chestnut  Arab  mare  that  its  right  to 
be  regarded  as  a  hybrid  has  been  questioned.  Matopo, 
however,  proved  so  impressive  that  all  his  hybrid  offspring 
plainly  indicated  their  descent  from  a  richly  striped 
zebra. 

"  On  the  other  hand,  the  subsequent  foals  (by  Arab 
and  other  stallions  out  of  the  mares  which  proved  fertile 
with  Matopo)  differed  so  profoundly  from  hybrids  (even 
when,  as  was  sometimes  the  case,  they  had  bars  on  the 
legs  and  faint  stripes  across  the  withers)  that  they  afforded 
no  evidence  that  the  first  male  influences  '  the  progeny 
subsequently  borne  by  the  mother  to  other  males.'  ' 

Baron  de  Parana  in  Brazil  produced  many  zebra 
hybrids  also  from  a  true  Burchell  zebra,  later  rearing  pure 
horse  foals  from  mares  that  had  previous  zebra  hybrids. 
In  no  single  case  did  the  stripes  which  did  sometimes 
appear  resemble  closely  the  striping  of  the  zebra. 

A  somewhat  extended  inquiry  by  Romanes  in  1893 

1  Ewart,  "The  Principles  of  Breeding  and  the  Origin  of  Do- 
mesticated Breeds  of  Animals,"  Report  of  the  Bureau  of 
Animal  Industry,  U.  S.  Dept.  of  Agr.,  1910. 


170  THE   BREEDING   OF   ANIMALS 

in  British  and  American  live-stock  journals  .developed 
the  fact  that  telegony  is  not  as  generally  believed  among 
breeders  of  the  present  day  as  has  been  generally  reported. 
Sir  Everett  Millais,  as  the  result  of  over  fifty  experiments 
with  mammals  and  birds,  found  no  conclusive  evidence 
of  infection. 

Evidences  of  telegony,  if  it  exists  at  all,  ought  to  be 
easily  collected  in  those  regions  where  the  production  of 
mules  is  common.  Darwin  says,1  "It  is  worthy  of  note 
that  farmers  in  South  Brazil  (as  I  hear  from  Fritz  Miiller) 
and  at  the  Cape  of  Good  Hope  (as  I  have  heard  from  two 
trustworthy  correspondents)  are  convinced  that  mares 
which  have  once  borne  mules  when  subsequently  put  to 
horses  are  extremely  liable  to  produce  colts  striped  like 
a  mule." 

These  conclusions  are  not  supported  by  Baron  de 
Parana,1  who  reports,  "  I  have  many  relatives  and  friends 
who  have  large  establishments  for  the  rearing  of  mules 
where  they  obtain  400  to  1000  mules  in  a  year.  In  all 
these  establishments,  after  two  or  three  crossings  of  the 
mare  and  ass,  the  breeders  cause  the  mare  to  be  put  to  a 
horse  because  they  believe  that  unless  the  mares  are 
changed  after  producing  three  mules  they  become  sterile. 
In  all  these  establishments  a  pure-bred  foal  has  never 
been  produced  resembling  either  an  ass  or  a  mule." 

160.  Telegony  and  mule  hybrids.  —  In  the  horse- 
breeding  districts  of  Missouri,  large  numbers  of  mules 
are  produced  annually.  Many  of  the  mares  which  have 
produced  one  or  more  mules  are  later  bred  to  stallions 
and  thus  become  the  dams  of  horse  foals.  The  jack 
and  the  stallion  differ  so  widely  in  many  important 
particulars  that  any  marked  tendency  of  horse  foals  to 

1  Report  of  the  Bureau  of  Animal  Industry,  1910,  p.  123. 


PLATE  X.  —  Upper.  Illustrating  a  condition  favorable  to  the 
appearance  of  telegony  in  horses.  This  mare  produced  seven  mule 
foals  and  then  the  mare  shown  below.  Lower.  The  dam  of  this  mare 
produced  seven  mule  foals  previous  to  the  birth  of  this  animal. 


PLATE  XI. —  Upper.  "Hallie,"  the  eleventh  foal  of  the  dam 
"Maude"  —  the  latter  having  previously  given  birth  to  ten  mule  foals 
in  succession.  Lower.  "Maude,"  dam  of  "Hallie,"  produced  ten 
mule  foals  previous  to  birth  of  "Hallie." 


INHERITANCE   OF  ACQUIRED   CHARACTERS     171 

resemble  a  previous  jack  sire  would  be  quickly  observed. 
The  writer  l  and  C.  B.  Hutchison  made  an  investigation 
of  a  large  number  of  the  horse  offspring  of  mares  which 
had  previously  foaled  mule  progeny  from  jack  sires. 
Many  of  the  horse  foals  examined  were  from  mares  that 
had  produced  more  than  one  mule.  In  one  case  a  mare 
had  given  birth  to  thirteen  mule  foals  in  succession  and 
had  then  produced  a  horse  foal.  Many  similar  cases 
gave  opportunity  to  observe  a  number  of  examples  in 
connection  with  which  full  and  favorable  opportunity 
was  present  for  the  display  of  the  influence  of  a  previous 
impregnation.  If,  as  some  believe,  the  influence  of  a 
previous  impregnation  is  cumulative  and  the  dam  becomes 
more  and  more  completely  infected  by  successive  matings, 
these  results  should  give  an  excellent  opportunity  to 
obtain  some  evidence  on  the  theory  of  "  infection  "  or 
"  saturation.'1 

A  total  of  168  mares  were  located  that  had  given  birth 
to  mule  foals  and  later  had  produced  horse  foals.  Of 
this  number  108  produced  their  first  foal  to  a  jack  and 
later  gave  birth  to  horse  foals.  Among  the  number  were 
forty  mares  that  produced  their  first  foals  to  a  stallion, 
later  producing  mule  foals  and  then  again  horse  foals. 
The  remainder  were  bred  in  a  somewhat  irregular  manner, 
but  all  were  alike  in  having  produced  horse  foals  following 
mule  foals.  The  number  of  mares  producing  one  or  more 
mule  foals  each  followed  in  every  case  by  horse  foals  was 
as  follows :  Eighteen  males  produced  one  mule  foal  each, 
followed  by  a  horse  foal ;  twenty-two  mares  produced 
two  mule  foals  each,  followed  by  a  horse  foal;  twelve 
mares  produced  three  mule  foals  each,  followed  by  a 

1  Mumford  and  Hutchison,  Unpublished  Data  of  the  Missouri 
Experiment  Station. 


172  THE  BREEDING  OF  ANIMALS 

horse  foal;  twenty  mares  gave  birth  to  four  mule  foals 
each,  followed  by  a  horse  foal;  eight  mares  gave  birth 
to  five  foals  each,  and  later  to  horse  foals;  ten  mares 
observed  produced  six  mule  foals  each,  and  afterward 
gave  birth  to  horse  foals;  seven  mares  produced  seven 
mule  foals  followed  by  horse  foals;  five  mares  produced 
horse  foals  after  having  foaled  eight  mules  each,  two  mares 
dropped  ten  mules  each,  followed  by  horse  foals;  while 
one  mare  produced  ten  mule  foals  and  then  a  horse  foal 
and  one  mare  was  bred  to  a  stallion  and  produced  a  healthy 
horse  foal  after  having  given  birth  to  thirteen  mule  foals 
in  succession. 

161.  Example  of  horse  foals.  —  The  horse  foals  from 
these  mares  were  carefully  examined  and  measured  for 
the  purpose  of  discovering  any  possible  resemblances 
to  the  previous  jack  sire  from  which  mules  had  been 
produced.  The  chief  external  characters  which  dis- 
tinguish the  mule  from  the  horse  are  the  size  and  form  of 
the  ears,  head,  feet,  legs,  body,  mane,  tail,  disposition  and 
voice. 

The  illustrations  of  dams  and  offspring  give  a  fairly 
adequate  idea  of  the  generally  uniform  nature  of  the 
results  which  were  found  throughout  the  investigation. 

In  Plate  X,  lower,  is  shown  the  yearling  offspring  of  a 
mare  (Plate  X,  upper)  that  had  previously  produced  seven 
mule  foals  and  then  gave  birth  to  the  animal  shown  in  the 
illustration.  A  careful  examination  of  the  characters  in 
which  mules  and  horses  differ  showed  that  the  offspring 
in  this  case  had  small,  rather  short,  smooth  head,  small, 
short,  pointed  ears,  a  broad  flat  foot  and  rather  broad 
hips  and  loins,  with  a  well-rounded  body.  None  of  the 
characters  of  this  yearling  colt  suggested  in  the  slightest 
degree  any  evidence  that  it  had  been  influenced  by  the 


PLATE  XII.  —  Upper.  "Sallie,"  the  ninth  foal  following  eight  mule 
foals  from  same  dam.  Lower.  The  dam  of  this  foal  produced  three 
horse  foals,  then  eight  mule  foals  and  the  animal  shown  in  this  illustration. 


PLATE  XIII.  —  Upper.  "Crewdson. "  A  condition  favorable  to  the 
appearance  of  telegony.  Previous  to  the  birth  of  this  mare  her  dam  (Kate) 
had  given  birth  to  eleven  mule  foals  in  succession.  Lower.  "Kate," 
mother  of  eleven  mule  foals  in  succession,  and  later  of  "Crewdson." 


INHERITANCE   OF  ACQUIRED   CHARACTERS     173 

fact  of  its  dam  having  previously  produced  seven  mule 
foals. 

"  Sallie  "  (Plate  XII,  upper)  was  foaled  by  a  saddle  bred 
mare  fifteen  years  old  and  was  the  ninth  foal  from  this 
mare.  The  previous  eight  foals  were  all  mules.  The  mare 
"  Sallie  "  was  characterized  by  a  small  refined  head  of 
good  quality,  a  small,  short  and  pointed  ear,  rather  scanty 
mane  and  tail,  fine  bone,  broad  and  rounded  foot  and  quiet 
and  gentle  disposition. 

The  mare  "  Hallie  "  shown  in  Plate  XI  was  sired  by  a 
Standardbred  stallion  from  the  dam  "  Maude  "  (Plate  XI, 
lower).  Maude  had  previously  given  birth  to  ten  female 
mule  foals.  At  two  years  of  age  "  Hallie  "  weighed  800 
pounds,  was  fifteen  hands  high,  had  a  short,  small,  refined 
head,  short  pointed  ears,  heavy  and  long  mane  and  tail, 
broad  flat  foot  and  a  rounded  body.  All  of  the  external 
characters  of  this  mare  were  clearly  horse  characters  and 
not  mule  characters.  There  was  no  suggestion  of  any 
resemblance  to  the  mule  in  any  of  its  characters. 

"  Crewdson  "  (Plate  XIII,  upper),  three  years  old,  was 
sired  by  a  Hackney  stallion  from  the  dam  "  Kate  "  (Plate 
XIII,  lower),  the  latter  having  given  birth  to  eleven  mule 
foals  followed  by  the  horse  foal  "  Crewdson."  This 
animal  was  sixteen  and  one-half  hands  high  and  weighed 
1000  pounds.  The  head  was  small  and  narrow,  ear 
short  and  small,  mane  and  tail  medium  heavy,  foot  broad 
and  flat.  "  Crewdson "  was  characterized  by  a  heavy 
mane  and  tail,  small  ear,  refined  head  and  broad  rounded 
foot. 

The  cases  cited  and  the  illustrations  used  were  selected 
because  it  was  assumed  that  if  the  influence  of  a  previous 
impregnation  was  likely  to  be  exhibited  at  all  it  would 
appear  in  those  dams  which  had  produced  a  large  number 


174  THE  BREEDING  OF  ANIMALS 

of  mules  followed  by  horse  foals.  No  such  evidence  could 
be  discovered.  The  168  horse  offspring  from  mares 
which  had  previously  produced  from  one  to  thirteen  mule 
foals  each,  gave  no  visible  evidence  of  the  existence  of 
telegony.  The  external  characters  of  the  mule  hybrid 
and  the  horse  differ  so  widely  in  many  important  partic- 
ulars that  even  a  slight  influence  which  might  come 
through  a  previous  sire  should  have  been  measurable. 

It  is  true  that  the  evidence  is  all  negative,  but  it  is 
nevertheless  valuable  because  of  the  peculiarly  favorable, 
opportunity  for  the  influence  of  telegony  to  assert  itself. 
It  is  also  interesting  to  note  in  this  connection  that  a 
belief  in  the  possible  influence  of  a  previous  impregnation 
is  by  no  means  universal  among  practical  breeders,  if 
we  may  judge  from  the  statements  of  farmers  in  the  mule- 
breeding  districts  of  Missouri.  Very  few  breeders  believed 
in  the  existence  of  telegony.  Those  who  admitted  their 
belief  in  the  possibility  of  infection  were  unable  to  cite 
authentic  instances. 

162.  Possibility  of  influence  from  a  previous  impregna- 
tion. —  If  the  influence  of  the  male  is  not  confined  to 
his  immediate  offspring  but  is  extended  to  the  mother 
in  such  a  way  that  other  progeny  by  other  males  may 
display  some  of  the  characters  of  the  former  male,  then 
such  influence  must  come  about  in  one  of  two  ways. 
The  body  (soma)  of  the  mother  herself  may  be  so  funda- 
mentally changed  by  acquiring  the  characters  of  the  male 
that  she  transmits  such  influence  to  her  succeeding  off- 
spring sired  by  other  males.  The  spermatozoa  of  the 
male  may  not  only  fertilize  the  fully  mature  and  thus 
susceptible  ovum  but  may  travel  through  the  generative 
organs  of  the  female  and  eventually  reach  the  ovaries 
where  the  developing  and  immature  eggs  might  be  so 


INHERITANCE   OF  ACQUIRED   CHARACTERS     175 

influenced  that  at  a  later  time  the  fully  fertilized  egg 
would  exhibit  the  results  of  fertilization  by  spermatozoa 
from  two  different  males.  The  possibility  of  such  double 
fertilization  is  extremely  remote.  The  known  facts 
regarding  the  successful  fertilization  of  the  egg  are  all 
against  such  an  hypothesis.  The  egg  is  probably  not 
susceptible  to  fertilization  by  the  sperm  except  during 
a  comparatively  brief  period  which  is  coextensive  with 
the  heat  period  in  the  domestic  animals.  The  immature 
ova  still  structurally  a  part  of  the  ovary  are  not  in  proper 
condition  to  be  fertilized.  The  probabilities  are  all 
against  any  such  influence  from  this  source. 

Is  it  possible  that  the  characters  of  the  male  may 
become  impressed  upon  the  pregnant  female  through  the 
influence  of  the  foetus  ?  If  the  body  (soma)  of  the  female 
is  influenced  in  this  way  is  this  influence  of  such  a  nature 
that  it  can  be  impressed  upon  the  embryo  in  the  uterus  ? 
If  it  can,  then  the  characters  of  a  previous  male  may 
affect  the  later  offspring  by  other  males.  Here  again  we 
must  admit  that  the  period  of  gestation  may  change  the 
body  of  the  mother  to  some  extent,  but  it  is  extremely 
improbable  that  such  change  influences  the  offspring  in 
any  hereditary  sense.  As  Rabaud 1  says,  "  Gestation 
naturally  produces  in  the  female  a  modification  which 
we  must  suppose  to  be  to  some  extent  permanent.  As 
a  consequence,  the  female  which  produces  a  second  off- 
spring is  no  longer  the  female  that  produced  the  first 
offspring;  whether  the  two  gestations  be  due  to  the 
same  male  or  to  two  different  males,  the  foetus  of  the  sec- 
ond gestation  evolves  in  conditions  different  from  those 
surrounding  the  foetus  of  the  first  gestation.  But  it  does 

1  Etienne  Rabaud,  "Telegony,"  The  Journal  of  Heredity, 
vol.  5,  p.  389. 


176  THE  BREEDING   OF  ANIMALS 

not  undergo  in  any  way  the  influence  of  the  first  male; 
in  reality,  what  takes  place  is  as  if  two  different  females 
were  involved,  mated  with  the  same  male  or  with  two 
different  males." 

The  conclusion  seems  very  plain  that  the  practical 
breeder  has  little  interest  in  the  subject  of  telegony. 
While  it  is  difficult  or  impossible  to  prove  by  direct 
experiment  that  telegony  does  not  exist,  it  is  also  true 
that  no  one  by  direct  experiment  has  ever  been  able  to 
produce  any  result  which  could  not  be  explained  on  some 
other  basis  than  that  of  telegony.  All  of  the  supposed 
cases  of  telegony  can  likewise  be  explained  on  some  other 
basis  than  the  assumption  that  a  previous  impregnation 
is  lasting  in  its  effect  and  may  influence  subsequent  off- 
spring. 

163.  Xenia  in  animals.  —  In  plants  the  effect  of  cross- 
pollination  in  certain  cases  is  to  be  observed  in  the  fruits. 
Gardeners  have  long  believed  that  the  watermelons  and 
citrons  should  not  be  planted  in  near-by  locations  because 
the  pollen  from  the  citron  would  injure  the  quality  of 
the  melon.  Such  injury  really  does  not  occur  in  this 
particular  case  but  similar  effects  are  present  in  other 
plants.  When  ordinary  white  corn  is  fertilized  with 
pollen  from  a  black  variety,  the  grains  so  pollinated  are 
black  or  mottled  while  other  grains  on  the  same  ear  are 
white.  An  explanation  for  this  phenomenon  is  to  be 
found  in  the  fact  that  there  are  two  cell  nuclei  in  the  ovum 
and  two  nuclei  in  the  pollen  cell.  The  primary  nuclei 
of  the  two  cells  unite  to  form  the  daughter  nucleus  of  the 
new  cell.  The  two  secondary  nuclei  likewise  unite  in 
the  formation  of  the  endosperm.  In  the  case  of  cross- 
pollination  of  black  and  white  corn  it  is  the  color  of  the 
endosperm  which  exhibits  the  influence  of  the  crossing. 


INHERITANCE   OF  ACQUIRED   CHARACTERS     177 

Among  mammals  the  highly  imaginative  idea  has  been 
suggested  that  the  influence  of  the  male  on  the  female 
(infection)  may  in  turn  be  passed  on  to  a  later  male  mated 
with  the  infected  female.  A  highly  successful  breeder 
of  Shorthorn  cattle  in  England  pointed  out  to  the  author 
a  pure-bred  white  cow  with  red  ears  from  a  registered 
sire  and  dam.  This  cow  was  marked  like  the  wild  white 
cattle  of  Chillingham  Park,  and  her  owner  ascribed  her 
markings  to  the  fact  that  her  dam  had  once  dropped  a 
calf  from  a  Chillingham  bull.  The  cause  of  the  peculiar 
markings  of  the  cow  in  this  case  could  not  have  been 
derived  in  the  manner  described.  The  case  is  cited  here 
only  as  an  example  of  the  highly  improbable  notion  that 
there  is  some  relation  between  the  phenomena  of  teleg- 
ony  and  xenia.  Xenia  among  mammals  is  unknown. 

164.  Xenia  among  poultry.  —  Many  breeders  of  poultry 
have  believed  that  the  eggs  of  the  domestic  fowl  may  be 
influenced  in  size,  form  and  color  by  the  male  bird. 
Observations  by  Nathusius  and  later  by  Holdefleiss 1 
gave  evidence  of  paternal  influence  on  the  color  of  the 
eggshell.  Holdefleiss  mated  Plymouth  Rock  hens  with 
a  Leghorn  cock.  The  Plymouth  Rock  uniformly  lays 
brown  eggs  while  the  Leghorn  lays  a  pure  white  egg. 
The  eggs  deposited  by  the  Plymouth  Rock  hens  from  this 
mating  varied  in  color  from  dark  brown  to  white.  The 
evidence  seemed  so  clear  to  the  investigator  that  he  was 
led  to  conclude  that  "  The  color  of  eggshells  shows  the 
influence  of  the  paternal  strain ;  there  is  therefore  evidence 
of  xenia."  More  recently  Walther  2  of  Giessen  after  a 
series  of  careful  experiments  has  reported  results  which 

1  Holdefleiss, "  Berichte  aus  dem  biologische  Lab.,"  Univ.  Halle, 
1911. 

2  Walther,  "Landwirthschaftliche  Jahrbiicher,"  1914. 

N 


178  THE  BREEDING   OF  ANIMALS 

do  not  confirm  those  of  Nathusius  and  Holdefleiss.  Wal- 
ther's  investigations  included  not  only  color  but  also 
size,  form  and  glossiness.  His  conclusions  were  that 
the  paternal  parent  has  no  influence  on  the  size,  shape 
and  glossiness  of  the  eggs.  His  results  on  the  color  of 
eggs  are  not  conclusive  but  tend  to  discredit  the  theory 
of  xenia  in  fowls.  From  all  the  evidence  available,  it 
would  seem  that  the  possibility  of  xenia  in  fowls  is  not 
satisfactorily  determined,  and  further  investigation  is 
needed  to  settle  this  supposed  influence  of  the  male  bird 
on  the  color  of  eggs. 

OBJECTIONS  TO  THE  THEORY  THAT  ACQUIRED  CHARACTERS 
ARE    TRANSMITTED 

The  trend  of  opinion  of  modern  biologists  has  been 
further  and  further  away  from  the  belief  in  the  possibility 
of  the  inheritance  of  acquired  characters.  As  our  knowl- 
edge of  cellular  biology  has  increased  and  we  have  been 
able  to  study  the  mechanical  processes  which  are  concerned 
in  reproduction  and  heredity,  it  has  become  more  and 
more  apparent  that  Weismann's  view  of  the  essential 
separateness  of  the  soma-cells  and  germ-cells  is  sub- 
stantially correct. 

165.  No  mechanism  for  the  inheritance  of  acquired 
characters.  —  There  is  no  mechanism  by  means  of  which 
somatic  modifications  may  impress  themselves  funda- 
mentally upon  the  germ-plasm.  In  fact,  the  develop- 
ment of  the  soma-cells  is  made  possible  by  determiners 
in  the  germ-cell.  The  very  fact  that  the  soma-cells 
have  been  able  to  respond  to  external  influences  and 
develop  in  a  direction  somewhat  different  from  the  average 
of  the  species  is  sufficient  evidence  that  the  determiners 


INHERITANCE   OF  ACQUIRED   CHARACTERS     179 

which  were  responsible  for  the  tendency  of  the  organism 
to  develop  in  the  given  direction  were  already  present 
in  the  germ-plasm.  As  Walter  aptly  remarked,  "  Not 
only  the  development  of  the  race  which  we  call  evolution, 
but  also  the  determination  of  the  individual  in  heredity, 
is  a  chain  of  onward-moving  sequences  like  the  succession 
of  events  in  history.  It  is  hard  to  see  how  recent  events 
can  influence  preceding  events.  It  is  hard  to  see  how 
the  water  that  has  gone  over  the  dam  can  return  and 
affect  the  flow  of  the  river  upstream  in  any  direct  way. 
It  is  likewise  hard  to  see  how  differentiated  somatoplasm, 
which  represents  the  end  stage  of  a  successive  series  of 
modifications,  can  make  any  definite  impress  upon  the 
original  germplasmal  sources  from  which  it  arose."  1 

Even  Darwin  found  difficulty  in  believing  in  the  inheri- 
tance of  acquired  characters.  His  theory  of  pangenesis 
which  assumed  that  each  somatic  cell  added  to  the  cir- 
culation a  minute  granule  which  later  found  its  way  to 
the  germ-plasm  is  not  substantiated  by  later  investiga- 
tions. 

The  evidence  presented  to  prove  that  somatic  modi- 
fications are  actually  transmitted  from  parent  to  offspring 
is  not  conclusive.  It  is  certain  that  acquired  characters 
cannot  be  transmitted  unless  the  germ-plasm  has  been 
definitely  changed  by  reason  of  somatic  influence.  The 
evidence  of  such  influence  upon  the  germ-cell  is  entirely 
negative.  Definite  experiments  carefully  planned  for 
testing  the  possible  effect  of  such  influence  have  been 
inconclusive. 

166.  The  inheritance  of  disease.  —  The  earlier  writ- 
ings on  animal  breeding  contain  numerous  references  to 
the  possibility  of  inheritance  of  disease.  Many  examples 

1  Walter,  "Genetics,"  1913,  p.  85. 


180  THE  BREEDING  OF  ANIMALS 

are  recorded  among  the  domestic  animals  of  supposed 
cases  of  the  heredity  of  pathological  conditions.  Among 
the  diseases  which  have  been  regarded  as  hereditary  are 
tuberculosis,  melanosis,  broken  wind,  specific  ophthalmia, 
blindness,  spavin,  ringbone,  curb  and  many  other  diseases. 
The  discussion  of  the  transmission  of  diseased  conditions 
of  the  organism  brings  forward  again  the  entire  question 
of  the  possible  inheritance  of  acquired  characters.  In 
general  it  may  be  said  that  recent  researches  in  biology 
have  resulted  in  demonstrating  that  many  diseases  which 
were  formerly  regarded  as  transmissible  are  no  longer 
believed  to  be  transmitted  through  inheritance.  This 
certainly  applies  to  all  diseases  which  are  contracted 
after  birth.  Some  diseases  which  are  the  result  of  a 
definite  variation  in  the  germ-plasm  will  of  course  be 
transmitted.  We  must  therefore  clearly  distinguish 
between  inborn  disease  and  acquired  disease.  Certain 
diseases  or  defects  are  undoubtedly  transmitted  from 
parent  to  offspring.  Whenever  such  defects  represent 
changes  in  the  germ-plasm,  then  such  defects  will  be  as 
certainly  transmitted  as  any  other  character  of  the  animal. 

Such  defects  which  may  be  transmitted  are  deaf- 
ness, color-blindness,  idiocy  and  possibly  rheumatism, 
gout  and  insanity.  In  the  latter  diseases  their  apparent 
transmissibility  may  be  the  result  only  of  a  predisposition. 

167.  Acquired  diseases.  —  Many  diseases  of  the  do- 
mestic animals  are  acquired  after  birth.  A  large  number 
of  pathological  diseases  are  due  to  infection.  All  such 
diseases  are  no  more  certainly  transmitted  than  are  other 
acquired  characters.  Tuberculosis  is  the  result  of  infec- 
tion by  a  specific  germ  and  this  germ  may  be  acquired 
under  certain  conditions  by  the  animal  organism.  In 
the  case  of  bone  diseases  of  horses,  which  were  for  a  long 


INHERITANCE  OF  ACQUIRED   CHARACTERS     181 

time  held  to  be  inherited,  it  is  probable  that  the  develop- 
ment of  such  unsoundness  is  due  largely  to  the  action  of 
external  factors.  In  other  words,  they  are  acquired.  It 
is  true,  however,  that  certain  individual  animals  or 
families  are  much  more  subject  to  bone  disease  than  other 
families.  In  such  case  we  must  recognize  a  predisposition 
to  disease. 

168.  Congenital  disease.  —  The  fact  that  a  disease 
exists  at  birth  is  not  always  adequate  evidence  that 
disease  has  been  inherited.     It  is  possible  for  certain  germ 
diseases  to  infect  the  foetus  in  utero.     It  is  also  probable 
that  the  ova  or  spermatozoa  may  under  certain  conditions 
carry  the  infection  and  this  infection  may  be  present  and 
active  during  the  prenatal  life  of  the  animal. 

169.  Predisposition  to  disease.  —  Many  diseases  ap- 
pear to  "  run  in  families."     For  this  reason  we  have  recog- 
nized the  fact  that  the  members  of  certain  families  are 
subject   to   tuberculosis,   gout,   rheumatism,   imbecility, 
insanity  or  other  diseases.     In  all  these  cases  there  exists 
a  predisposition  on  the  part  of  the  members  of  a  given 
family  to  acquire  the  diseased  condition.     Through  weak- 
ness of  certain  organs  or  general  lack  of  constitutional 
vigor,  the  infective  germs  of  many  diseases  may  overcome 
the  resistance  of  the  animal  organism  to  disease.     This 
predisposition  is  certainly  and  often  strongly  inherited. 
From  the  standpoint  of  the  practical  animal  breeder, 
therefore,  a  predisposition  to  disease  may  be  quite  as 
significant  as  the  actual  transmission  of  the  disease. 

170.  Immunity.  —  An    interesting    correlated    fact    is 
the    probable    inheritance    of    immunity    from    certain 
diseases.     Certain   families   seem   to   possess   immunity 
from  certain  diseases,  such  as  smallpox  or  diphtheria.     It 
is  not  possible  at  this  time  to  enter  into  a  discussion  as 


182  THE  BREEDING  OF  ANIMALS 

to  the  nature  of  immunity,  but  undoubtedly  the  known 
immunity  of  certain  individuals  or  families  to  certain 
diseases  may  become  the  basis  of  important  future  im- 
provements in  the  domestic  animals.  In  recent  years 
it  has  been  found  that  certain  hogs  are  immune  from  hog 
cholera.  Experiments  have  been  suggested  to  deter- 
mine whether  or  not  it  would  be  possible  to  develop  a 
race  of  swine  immune  to  this  dreaded  disease. 

It  is  possible  for  animals  to  acquire  immunity  through 
vaccination  of  actual  infection  of  the  disease  itself.  Such 
immunity  is  not  transmitted.  It  is  doubtful  whether 
there  exists  any  congenital  immunity,  but  investiga- 
tions along  this  line  might  be  fruitful  of  results. 


CHAPTER  IX 
HEREDITY  AND  SEX 

THE  chief  function  of  both  plants  and  animals  is  to 
live  and  reproduce.  In  many  wild  forms  the  powers  of 
reproduction  are  little  short  of  marvelous.  A  single 
plant  of  purslane  may  produce  a  million  seeds.  Man  is 
less  productive  than  most  other  mammals,  but  masses  of 
population  have  been  known  to  double  in  twenty-five 
years.  At  this  rate  in  1000  years  there  would  not  be 
standing  room  on  the  earth  for  his  children. 

The  natural  increase  of  plants  and  animals  is  not  real- 
ized because  of  unfavorable  conditions.  The  number 
of  animals  that  can  exist  on  a  given  area  is  limited.  If 
too  many  are  born,  some  must  inevitably  die.  Others 
are  destroyed  by  enemies,  while  still  others  are  poisoned 
by  substances  which  accumulate  within  their  own  bodies. 

The  kinds  of  reproduction  have  already  been  men- 
tioned under  the  general  subject.  The  simplest  form  of 
reproduction  is  by  cell  division.  This  method  of  repro- 
duction is  chiefly  found  in  unicellular  organisms  like  the 
amoeba  and  paramcecium.  The  most  common  method 
of  reproduction  is  by  eggs.  Egg  production  is  almost 
universal  among  both  plants  and  animals.  But  the  egg 
generally  is  inert  and  incapable  of  development  into  a 
new  individual  until  it  has  been  fertilized.  Herein  lies 
the  apparent  reason  for  differentiation  into  male  and 
female  sexes. 

183 


184  THE   BREEDING   OF  ANIMALS 

171.  The  significance  of  conjugation  and  fertilization. 
—  The  real  purpose  of  fertilization  is  not  well  under- 
stood. Biologists  are  not  yet  able  to  speak  with  positive 
assurance  as  to  the  real  character  of  the  actual  biological 
phenomena  which  result  from  conjugation  of  the  male 
and  female  germ-cells.  Butschli  believed  that  fertiliza- 
tion was  a  process  of  rejuvenation.  This  idea  involves 
the  assumption  that  the  union  of  the  germ-cells  of  two 
weak  individuals  will  result  in  the  production  of  a  strong 
individual. 

Jennings,  in  a  series  of  very  skillful  and  carefully  con- 
trolled experiments  with  paramoecium,  found  that  after 
conjugation  the  rate  of  division  was  not  accelerated  but 
was  actually  slower.  Paramoecium  which  had  been 
artificially  weakened  and  their  rate  of  division  retarded 
when  allowed  to  conjugate  was  not  in  most  cases  bene- 
fited. Some  were  apparently  benefited,  but  in  all  cases 
the  rate  of  division  was  slower  than  in  cultures  in  which 
the  paramoecium  was  well  nourished.  In  other  words, 
conjugation  was  of  advantage  to  some  and  not  to  others. 
Jennings  concluded  that  conjugation  is  for  the  purpose 
of  bringing  about  a  recombination  of  characters.  Some 
of  them  are  very  beneficial  and  will  persist  and  multiply, 
others  are  disadvantageous  and  these  will  fail  to  live  and 
reproduce.  The  combinations  most  likely  to  persist 
are  heterozygous. 

As  Morgan  l  has  explained,  "  The  meaning  of  conjuga- 
tion, and  by  implication,  the  meaning  of  fertilization  in 
the  higher  forms  is  from  this  point  of  view  as  follows : 
In  many  forms  the  race,  as  a  whole,  is  best  maintained 
by  adapting  itself  to  a  widely  varied  environment.  A 
heterozygous  or  hybrid  constitution  makes  this  possible, 

1  Morgan,  "Heredity  and  Sex,"  p.  12. 


HEREDITY   AND  SEX  185 

and  is  more  likely  to  perpetuate  itself  in  the  long  run 
than  a  homozygous  race  that  is  from  the  nature  of  the 
case  suited  to  a  more  limited  range  of  external  conditions." 
Whatever  may  be  the  real  nature  and  purpose  of  fertili- 
zation, it  is  certainly  true,  as  Wilson1  remarks,  that  "  the 
paternal  germ-cell  is  the  carrier  of  something  which 
incites  the  egg  to  development,  and  thus  constitutes  the 
fertilizing  element  in  the  narrower  sense." 

172.  Secondary    sexual    characters.  —  The    sexes    in 
the  higher  animals  are  differentiated,  not  alone  by  the 
possession  of  radically  different  essential  organs  of  repro- 
duction, but  also  by  the  possession  of  so-called  secondary 
sexual  characters.     The  more  brilliant  plumage  of  the 
male  bird,  the  horns  of  the  ram,  and  the  greater  develop- 
ment of  the  head  and  horns  of  the  bull  are  examples 
of  secondary  sexual   characters.     Darwin  regarded  the 
secondary  sexual  characters  as  of  great  significance  in 
sexual  selection.     As  a  result  of  sexual  selection  he  believed 
that  "  generally,  the  most  vigorous  males,  those  which 
are  best  fitted  for  their  places  in  nature,  will  leave  most 
progeny." 

173.  Secondary  sexual  characters  and  vigor.  —  Breed- 
ers of  the  domestic  animals  have  long  regarded  the  degree 
of  development  of  the  secondary  sexual  characters  as 
an  index  of  sexual  vigor.     Many  have  held  that  a  male 
with  the  secondary  sexual  characters  strongly  developed 
was  not  only  prepotent  in  the  transmission  of  purely 
sexual  characters  but  also  in  other  characters  which  are 
desirable  to  man.     Direct  evidence  is  not  available  to 
show  that  because  an  animal  is  strongly  developed  in  the 
secondary  sexual  characters,  he  is  therefore  prepotent 

1  Wilson,  "The  Cell,"  p.  230  (1911). 

2  Morgan,  "Heredity  and  Sex,"  p.  101. 


186  THE  BREEDING   OF   ANIMALS 

in  the  transmission  of  all  characters.  Sexual  vigor  is 
associated  with  the  development  of  the  secondary  sexual 
characters,  and  sexual  vigor  is  a  desirable  character  in 
the  domestic  animals.  The  general  efficiency  of  the 
reproductive  process  is  undoubtedly  correlated  with  the 
secondary  sexual  characters.  The  breeder,  therefore, 
is  making  no  mistake  in  emphasizing  the  importance  of 
evidences  of  strong  sexuality  as  indicated  by  the  develop- 
ment of  the  secondary  sexual  characters. 

174.  Effects  of  castration  and  ovariotomy  on  the 
secondary  sexual  characters.  —  There  is  ample  evidence 
of  the  close  correlation  existing  between  the  essential 
organs  of  sexual  reproduction  and  the  secondary  sexual 
characters.  The  full  development  of  the  secondary 
sexual  characters  is  closely  connected  with  sexual  maturity. 
In  the  Merino  breed  of  sheep,  the  males  are  always  horned 
while  the  females  are  hornless.  If  the  male  is  castrated 
before  the  horns  begin  to  develop,  the  horns  fail  to  grow 
and  the  wether  remains  hornless.  If  the  males  are 
castrated  after  the  horns  have  started  to  develop,  the 
horns  cease  to  grow.  Marshall,  in  experiments  with 
Herdwick  sheep,  a  breed  in  which  the  males  are  supplied 
with  large  coiled  horns  and  the  females  are  hornless,  found 
that  castration  at  varying  ages  invariably  caused  a 
cessation  in  the  growth  of  the  horns  of  the  male.  When 
the  ovaries  of  the  female  were  removed,  there  was  no 
apparent  tendency  toward  the  growth  of  horns,  although 
small  scurs  appeared  in  one  spayed  ewe  that  was  kept  for 
seventeen  months  after  removal  of  the  ovaries.  Marshall 
concludes,  "  The  development  of  horns  in  the  males  of 
a  breed  of  sheep  in  which  well-marked  secondary  sexual 
differentiation  occurs  (as  manifested  especially  by  presence 
or  absence  of  horns)  depends  upon  a  stimulus  arising  in 


HEREDITY  AND  SEX  187 

the  testes,  and  this  stimulus  is  essential,  not  merely  for  the 
initiation  of  the  horn  growth,  but  for  its  continuance,  the 
horns  ceasing  to  grow  whenever  the  testes  are  removed." 

"  The  removal  of  the  ovaries  from  young  ewes  belong- 
ing to  such  a  breed  does  not  lead  to  the  development  of 
definitely  male  characters,  except  possibly  in  an  extremely 
minor  degree."  1 

Arkell 2  crossed  Merino  ewes  with  a  Southdown  ram 
(hornless).  The  sons  of  this  cross  had  horns.  The 
factor  for  horns  in  this  case  must  have  been  present  in 
the  Merino  mother,  herself  hornless,  but  the  full  develop- 
ment of  horns  cannot  take  place  except  the  male  glands 
are  present  and  functional. 

175.  Effect  of  transplanting  sexual  glands.  —  The  in- 
vestigations already  described  seem  clearly  to  point  to  the 
conclusion  that  some  stimulus  to  the  development  of  the 
secondary  sexual  glands  exists  in  the  testes  and  ovaries. 

Steinach  transplanted  ovarian  tissue  from  a  female 
guinea  pig  to  the  tissues  of  a  castrated  male.  The  result 
was  to  cause  the  rudimentary  mammary  glands  of  the 
male  greatly  to  enlarge  and  the  male  came  to  resemble 
the  female  in  certain  characters.3 

A  remarkable  experiment  is  described  by  Goodale  4  in 
which  the  ovaries  of  a  female  Mallard  duck  were  entirely 
removed  and  the  plumage  became  like  that  of  the  male 
Mallard. 

176.  Effect    of    internal    secretion.  —  The    secretions 
of  various  internal   organs  have  a  profound   influence 
upon  the  development  of  the  individual.     These  secre- 

1  Marshall,  Proceedings  Royal  Society  (London),  ser.  B,  85, 
1912. 

2  Arkell,  New  Hampshire  Agr.  Exp.  Sta.,  Bui.  160. 

3  Morgan,  "  Heredity  and  Sex,"    1913,  p.  140. 

4  Goodale,  Journal  Experimental  Zoology,  10. 


188  THE   BREEDING   OF   ANIMALS 

tions,  called  "  hormones/'  emanate  from  various  glands 
and  perhaps  from  most  of  the  internal  organs.  If  the 
thyroid  and  parathyroid  bodies  are  removed  from  the 
body,  death  follows.  The  destruction  of  the  pituitary 
glands  in  man  causes  the  bones  of  the  hands,  feet  and  jaws 
to  enlarge  (gigantism),  causing  death. 

It  is  probable  that  the  milking  function  in  the  domes- 
tic animals  has  some  connection  with  the  activities  of  a 
specific  "  hormone  "  which  is  essential. 

177.  Sex-linked  characters.  —  Certain  characters  are 
so    closely    related    to    sex    that    their    transmission    is 
influenced    by    such    relation.     These    characters    have 
been  called  sex-linked  or  sex-limited  characters.     They 
are  to  be  distinguished  from  secondary  sexual  characters. 

178.  Color-blindness.  —  Men    are    much    more    fre- 
quently color-blind  than  women.     Color-blind  men  do 
not  transmit  color-blindness  directly  to  sons,  but  to  grand- 
sons through  their  daughters.     The  daughters  of  color- 
blind men  are  not  themselves  color-blind,  but  tend  to 
transmit  this  deficiency  to  their  sons.     Color-blindness 
in  the  daughter  could  be  produced  only  when  the  father 
was  color-blind  and  the  mother  possessed  the  power  to 
transmit  color-blindness.     Color-blindness  is  the  result  of 
some  defect  in  the  germ-cell.     This  factor  which  is  asso- 
ciated with  an  x  chromosome  appears  twice  in  the  ovum 
and  only  once  in  the  sperm.     A  similar  condition  is  found 
in  the  pomace  fly  1  (Drosophila  ampelophila).    This  form 
has  normally  red  eyes,  but  this  apparently  is  a  unit  char- 
acter,  sex-linked  in  transmission.     An  interesting  case 
of  sex-linked  heredity  is  found  in  the  Barred  Plymouth 
Rock  fowl.2    Pure  barred  fowls  when  mated  produce 

1  Castle,  "Heredity  and  Eugenics,"  p.  75. 

2  Castle,  "Heredity,"  1911,  p.  170. 


HEREDITY  AND  SEX  189 

only  barred  offspring.  When  the  male  Barred  Rock  is 
bred  with  a  non-barred  variety,  the  offspring  of  both 
sexes  are  all  barred.  If  the  female  Barred  Rock  is  mated 
with  non-barred  breed,  the  offspring  will  be  about  one- 
half  barred  and  the  remainder  non-barred.  The  barred 
offspring  are  always  males,  while  all  the  females  are  non- 
barred.  The  barred  character  is,  therefore,  sex-limited. 
The  Barred  Rock  female  is  heterozygous  and  the  male 
homozygous.  The  pure  Barred  Rock  breed  transmits 
the  barred  quality  because  the  male  is  pure  in  respect  to 
the  barred  character.  The  same  result  follows  if  a  cross- 
barred  male  is  mated  with  barred  females.  The  explana- 
tion of  sex-linked  inheritance  is  probably  to  be  found  in 
the  existence  of  some  plus  element  in  the  egg  which  is 
not  found  in  the  sperm. 

179.  Controlling  the  sex  of  offspring.  —  In  many  of 
the  domestic  animals,  the  sex  of  the  individual  determines 
its  peculiar  value  and  usefulness  to  mankind.     If  some 
method  of  breeding  could  be  devised  which  would  result 
in  the  production  of  the  particular  sex  desired,  it  would 
be  a  great  economic  gain.     That  such   attempts  have 
been  made  by  both  ancient  and  modern  breeders  is  made 
clear  from  an  examination  of  the  literature  of  the  subject 
from  the  earliest  times  to  the  present.     Because  of  the 
more  or  less  general  belief  among  practical  breeders  in 
the  possibility  of  controlling  sex,  it  seems  necessary  to 
consider  briefly  some  of  the  more  widely  held  theories  of 
sex  control. 

180.  Age   or  vigor  of  parents.  —  Two  investigators, 
Sadler  l  (1830)  in  England  and  Hofaker  (1823)  in  Ger- 
many, collected  statistics   representing  more  than  2000 
births.    Their  statistics  showed  that  when  the  father  is 

1  Carpenter,  "Human  Physiology,"  p.  1015. 


190 


THE   BREEDING  OF  ANIMALS 


older  the  larger  number  of  the  offspring  are  males,  and 
when  the  mother  is  older  the  children  tend  to  be  females. 
These  results  have  been  confirmed  by  Gohlert,  Boulanger 
and  Legoyt.  Many  practical  breeders  have  also  cited 
special  cases  in  which  the  sex  offspring  seemed  to  follow 
that  of  the  older  parent.  Giroude  Buzareingues  l  reports 
results  from  breeding  young  immature  ewes  to  strong 
mature  rams.  The  proportion  of  sexes  was  80  males 
to  35  females.  When  young  rams  were  used  as  sires, 
the  proportion  of  sexes  was  53  males  and  84  females. 

SUMMARY  OF  STATISTICS  BEARING  ON  RELATIVE  NUMBER 
OF  MALES  AND  FEMALES  2 


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Hofaker 

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Tubingen 

117.8 

92.0 

90.6 

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Sadler 

2,068 

England 

121.4 

94.8 

86.5 

114.7 

— 

Gohlert 

4,584 

England 

108.0 

93.2 

82.6 

105.3 

— 

Legoyt 

52,311 

Paris 

104.49 

102.14 

97.5 

102.97 

— 

Boulanger 

6,006 

Calais 

109.98 

107.92 

101.63 

107.9 

— 

Noirot 

4,000 

Dijon 

99.7 

— 

116.0 

103.5 

— 

Breslau 

8,084 

Zurich 

103.9 

103.1 

117.6 

186.6 

— 

Stieda 

100,590 

Alsace- 

Lorraine 

105.03 

— 

108.39 

106.27 

Contra- 

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Berner 

267,946 

Sweden 

104.61 

106.23 

107.45 

106.0 

Contra- 

dictory 

1  Quarterly  Journal  of  Agriculture,  vol.  1,  1828,  p.  63. 

2  Geddes  and  Thompson,  "The  Evolution  of  Sex,"  p.  35. 


HEREDITY  AND  SEX  191 

The  differences  are  not  large  and  the  number  of  observa- 
tions are  entirely  too  few  to  justify  any  sweeping  conclu- 
sions. Steida  1  and  Berner  found  no  relation  between 
age  and  the  sex  of  offspring.  The  evidence  of  the  in- 
fluence of  age  on  the  sex  of  offspring  is  too  conflicting  to 
be  conclusive. 

181.  Comparative  vigor  or  sexual  superiority.  —  Vari- 
ous authorities  have  attempted  to  explain  the  proportion 
of  sexes  on  the  theory  that  the  sex  of  the  offspring  will 
correspond  to  that  of  the  more  vigorous  or  "  superior  " 
parent.     Darwin,  Richarz,  Hough  and  others  regarded 
the  male  as  to  a  certain  extent  a  superior  organization, 
and  male  offspring  would  result  when  the  reproductive 
functions  of  the  mother  were  particularly  well  developed. 
The  evidence  available  is  not  sufficient  to  give  this  hypoth- 
esis any  particular  importance  in  practical  breeding. 

182.  Nutrition  and  sex.  —  That  the  nutritive  condition 
of  the  parents,  particularly  the  mother,  at  the  time  of 
fertilization  and  before    has  a  preponderating  influence 
on  the  sex  of  offspring  has  been  long  believed.     Yung 
found  that  under  certain  conditions  regarded  as  normal, 
the  proportion  of  sexes  in  tadpoles  was  about  57  females 
to  100  males.     By  feeding  the  tadpoles  beef,  fish  and 
frog's  flesh,  the  percentage  of  females  enormously  in- 
creased, being  in  one  case  92  females  to  8  males.     An 
interesting  case  illustrating  the  connection  of  nutrition 
and  sex  is  found  in  bees.     The  swarm  of  bees  is  composed 
of  workers  (imperfect  females),  drones  (males)  and   the 
queen  (a  perfect  female).    The  drones  are  hatched  from 
unfertilized  eggs.     The  queen  and  workers  are  developed 
from  fertilized  eggs,  but  perform  a  very  different  role  in 
life.     The  queen  becomes  the  mother  of  new  generations, 

1  Ibid. 


192  THE  BREEDING  OF  ANIMALS 

while  the  worker  bees  are  sexually  imperfect.  It  seems 
to  be  true  that  the  eggs  developing  into  worker  bees 
and  queens  are  identical.  The  one  becomes  a  queen  as 
the  result  of  a  "  royal  "  diet,  while  the  worker  larvae 
are  fed  on  a  "  common  "  diet  and  develop  into  the  non- 
fertile  female.  Investigations  with  wasps  by  Von  Siebold  l 
and  butterflies  and  moths  by  Mrs.  Treat  suggest  a  real 
connection  between  nutrition  and  sex  offspring.  Schenk 
found  that  starvation  produced  fewer  males,  but  later 
the  same  condition  resulted  in  producing  more  males. 
Busing  reported  that  among  the  Swedish  nobility  the 
proportion  of  sexes  was  98  boys  to  100  girls,  and  in  the 
Swedish  clergy  108.6  boys  to  100  girls.  Punnett  submits 
evidence  that  in  London  more  girls  are  born  among  the 
poor  than  the  rich.  In  most  of  'the  cases  cited  there  are 
too  many  other  factors  involved  to  justify  the  conclusion 
that  nutrition  alone  is  responsible  for  the  proportion  of 
the  sexes. 

183.  The  maturity  of  the  ovum.  —  The  degree  of 
development  or  maturity  of  the  ovum  itself  at  the  time 
of  fertilization  has  a  controlling  influence  on  sex  in  the 
opinion  of  some  breeders.  If  fertilization  occurs  during 
the  early  part  of  the  heat,  the  offspring  will  be  female. 
If  the  ovum  is  fertilized  later  in  the  heat,  the  offspring 
will  tend  to  be  males.  Thus  Thury2  of  Geneva  says, 
"  The  sex  depends  upon  the  degree  of  maturity  of  the 
egg  at  the  moment  of  fecundation,  that  which  has  not 
reached  a  certain  degree  of  maturity  producing  the  female, 
and,  if  fecundated  when  this  point  of  maturity  has  passed, 
producing  a  male."  These  results  are  not  altogether 
consistent  with  ordinary  farm  practice  or  with  the  experi- 

1  Rolph,  W.  H.,  "Biologische  Probleme,"  Leipsig,  1884. 

2  Country  Gentleman,  1864,  p.  12. 


HEREDITY   AND  SEX  193 

ments  of  others.  In  ordinary  breeding  operations  on  the 
range,  the  bull  invariably  runs  with  the  cows  and  breed- 
ing occurs  during  the  first  part  of  the  heat.  If  the  sex 
is  determined  to  any  extent  by  the  particular  stage  of 
heat,  then  in  this  case  the  offspring  should  be  largely 
female.  But  such  is  not  the  case,  the  proportion  of  the 
sexes  is  practically  equal,  subject  to  seasonal  or  other 
variations  not  entirely  explainable.  Thury's  results 
have  not  been  satisfactorily  confirmed.  Miles  1  recorded 
the  proportion  of  sexes  among  cattle  and  sheep  on  the 
Michigan  Agricultural  College  farm  for  a  period  of  ten 
years.  The  results  were  as  follows:  Sheep,  102.5  males 
to  100  females.  Cattle,  118.4  males  to  100  females.  All 
the  animals  were  bred  during  the  first  part  of  the  heat 
and  the  offspring  should  have  been  more  largely  female. 
The  proportion  of  the  sexes  seems  to  be  subject  to  wide 
variation,  and  therefore  any  investigations  of  this  kind 
must  necessarily  include  large  numbers  of  animals  and 
the  observation  be  carried  over  a  series  of  years  to  make 
the  results  of  any  value. 

184.  Seasonal  variations  in  proportion  of  sexes.  — 
The  proportion  of  the  sexes  is  subject  to  wide  variations 
apparently  due  to  seasonal  influences.  Quoting  again 
from  Miles : 2 

"  In  1864  and  1865  the  bull-calves  were  2.5  to  1  heifer ; 
in  1866  and  1867  the  heifers  were  considerably  in  excess ; 
in  1868  and  1869  the  heifers  were  nearly  2  to  1  bulls ;  in 

1870  the  bulls  were  decidedly  more  numerous ;    and  in 

1871  and  1872  there  were  more  than  2  bulls  to  1  heifer. 
In  1872  there  were  2  rams  to  1  ewe,  and  the  bulls  were 
nearly  in  the  same  proportion  to  the  heifers,  which  would 

1  Miles,  "  Stock  Breeding,"  1878,  p.  265. 

2  Ibid.,  p.  299. 
o 


194  THE   BREEDING  OF  ANIMALS 

seem  to  indicate  some  peculiar  influence  of  the  season  in 
favor  of  the  males.  In  1871,  however,  the  bulls  were 
largely  in  excess  of  the  cow-calves,  and  there  was  quite 
as  decided  a  preponderance  of  females  among  the  sheep." 

185.  Sex  cannot  be  controlled  by  external  conditions. 
—  The  most  recent  investigations  of  sex  determination 
lead  to  the  belief  that  sex  is  predetermined  in  the  germ- 
cell.  It  is  not  subject  to  change  through  any  change  in 
the  environment,  as  nutrition  or  temperature.  The 
germ-cell  contains  a  determiner  for  sex  as  it  contains 
determiners  for  other  characters. 

Castle  concludes, l  "  If,  as  has  been  suggested,  the  deter- 
mination of  sex  in  general  depends  upon  the  inheritance 
of  a  Mendelian  factor  differentiating  the  sexes,  it  is  highly 
improbable  that  the  breeder  will  ever  be  able  to  control 
sex.  Male  and  female  zygotes  should  forever  continue 
to  be  produced  in  approximate  equality,  and  consistent 
inequality  of  male  and  female  births  could  result  only  from 
greater  mortality  on  the  part  of  one  sort  of  zygote  than 
of  the  other." 

The  same  idea  is  similarly  expounded  by  Morgan.2 
"  If  these  observations  are  confirmed,  they  show  that 
in  man,  as  in  so  many  other  animals,  an  internal  mechan- 
ism exists  by  which  sex  is  determined.  It  is  futile,  then, 
to  search  for  environmental  changes  that  might  determine 
sex.  At  best  the  environment  may  slightly  disturb  the 
regular  working  out  of  the  two  possible  combinations 
that  give  male  or  female.  Such  disturbances  may  affect 
the  sex  ratio  but  have  nothing  to  do  with  sex-determina- 
tion. 

1  Castle,  "Heredity,"  1911,  p.  180. 

2  Morgan,  "  Heredity  and  Sex,"  p.  248. 


CHAPTER  X 
VARIATION 

No  biological  fact  is  more  clearly  recognized  than  the 
tendency  of  all  plants  and  animals  to  vary.  In  a  broad 
way,  individuals  resemble  their  parents.  Through  hered- 
ity the  qualities  of  the  parent  are  transmitted  to  the  off- 
spring. A  horse  begets  other  horses  and  not  pigs.  We 
do  not  gather  grapes  of  thorns  nor  figs  from  thistles. 
Thus  has  come  about  the  old  adage  "  like  begets  like," 
but  this  aphorism  applies  only  within  certain  limits  and 
fails  to  take  into  account  the  inexorable  law  of  variation 
by  which  the  offspring  is  never  exactly  like  the  parent. 
It  is  true  that  the  offspring  of  a  horse  will  always  be  a 
horse  and  not  a  cow.  It  is  even  true  that  the  progeny  of 
a  trotting  horse  will  be  a  trotting  horse,  but  the  keen 
judge  of  horses  is  able  to  discern  slight  variations  in  form, 
color,  disposition  or  ability  to  perform. 

No  two  animals  are  exactly  alike.  The  difference 
may  be  slight  or  very  marked.  From  the  same  sire  and 
dam,  the  offspring  may  differ  widely  in  character  among 
themselves.  In  a  large  family  of  boys,  the  physical 
characters  and  mental  dispositions  of  the  individual 
members  of  the  family  may  be  very  different.  It  has 
happened  in  the  history  of  trotting  and  running  horses 
that  own  brothers  have  varied  widely  in  their  ability 
to  win  in  speed  competitions. 

195 


196  THE  BREEDING  OF  ANIMALS 

186.  Importance  of  variability.  —  The  inherent  tend- 
ency to  vary  which  exists  in  all  organic  beings  makes  the 
improvement    of    domestic    races    possible.     Inorganic 
compounds  are  fixed  in  composition  and  physical  char- 
acter.    Pure  gold  cannot  be  improved.     The  individual 
animal  has  within  its  own  organic  constitution  not  only 
the  capacity  for,  but  a  noticeable  tendency  toward,  varia- 
tion from  the  characters  of  its  ancestors.     This  fact  lies 
at  the  very  foundation  of  the  successful  improvement 
of  domestic  animals.     If  it  were  true  that  the  offspring 
was  identical  in  character  with  the  parent,  then  improve- 
ment would  be  impossible. 

In  developing  new  varieties,  the  breeders'  efforts 
are  sometimes  first  directed  toward  encouraging  the 
tendency  to  variation.  If  the  particular  form  which 
the  breeder  is  endeavoring  to  improve  possesses  an  unusual 
tendency  to  vary,  then  a  large  number  of  new  characters 
or  new  combinations  of  characters  will  occur.  Some  of 
these  will  be  desirable,  but  many  will  be  less  desirable 
than  in  the  parent  forms.  The  individuals  which  possess 
the  most  useful  and  valuable  characteristics  will  be  pre- 
served by  selection.  After  desirable  variations  have 
occurred,  the  next  step  is  to  fix  these  by  heredity  so  that 
they  may  become  racial  characteristics  and  be  trans- 
mitted with  some  degree  of  regularity  from  parent  to 
offspring. 

187.  Morphological  variations.  —  The  variations  which 
are  of  interest  to  the  animal-breeder  exhibit  many  differ- 
ent forms. 

Morphological  variations  are  those  affecting  the  form. 
These  may  be  merely  differences  in  size,  as  in  the  case 
of  two  pigs  possessing  the  same  characters  and  the  same 
relative  development  of  characters  but  differing  in  size. 


VARIATION  197 

Some  individuals  are  dwarfs  while  others  are  giants  in 
size.  This  variation  in  size  is  due  to  a  difference  in  the 
number  of  cells  rather  than  in  the  size  of  the  cells.  The 
increased  number  of  cells  found  in  the  larger  individuals 
represents  excessive  cell  division,  while  the  abnormally 
small  are  the  result  of  imperfect  and  arrested  cell  division.1 

The  cause  of  undersized  individuals  among  animals 
cannot  always  be  determined.  It  is  certain,  however, 
that  insufficient  food  or  food  which  is  deficient  in  the 
necessary  elements  of  nutrition  is  a  common  cause  of 
undersized  animals. 

It  is  also  true  that  when  females  become  pregnant 
while  still  growing  and  immature,  their  growth  receives 
a  sudden  check.  The  arrested  development  is  not  so 
much  due  to  the  effects  of  pregnancy  as  to  the  strain  of 
lactation.  The  growth  of  well-fed  females  is  probably 
not  to  any  appreciable  extent  checked  by  pregnancy, 
but  the  physiological  requirements  for  the  production 
of  milk  are  severe  and  the  development  of  immature 
mammalian  females  is  abruptly  arrested  during  the 
period  of  lactation. 

Differences  in  size  are  of  relatively  less  importance  than 
morphological  differences  arising  from  variation  in  the 
relative  development  of  the  parts  of  the  body.  This 
may  be  illustrated  by  the  variations  in  meat  animals. 
Beef  cattle  may  possess  a  broad  back,  well-sprung  rib, 
and  a  thick  covering  of  flesh  over  all  parts,  or  they  may 
lack  these  highly  desirable  qualities. 

188.  Physiological  variations.  —  Changes  in  the  func- 
tional activities  of  animals  are  frequent  and  important. 
The  average  domestic  cow  produces  not  more  than  150 
pounds  of  butter  in  a  year,  but  selected  herds  may  produce 

1  Davenport,  "Principles  of  Breeding,"  p.  27. 


198  THE   BREEDING  OF  ANIMALS^ 

500  pounds  of  butter  in  one  year.  Some  individuals 
are  very  fertile,  others  may  be  sterile  or  markedly  deficient 
in  this  very  desirable  quality. 

189.  Meristic  variation.  —  All  plants  or  animals  develop 
in  accordance  with  a  certain  symmetrical  pattern.  A 
quadruped  has  four  legs,  two  ears,  two  eyes,  and  two  sides 
of  similar  character.  A  deviation  from  the  characteristic 
plan  or  pattern  of  the  species  is  called  a  meristic  variation. 
Such  variations  are  of  very  great  importance  among 
plants,  but  are  of  little  practical  significance  to  the  animal- 
breeder.  Examples  of  meristic  variation  are  to  be  seen 
in  the  doubling  of  flowers,  the  stooling  of  grains,  and 
the  production  of  four-leaved  clovers.  Among  animals 
the  growth  of  extra  fingers  and  toes,  and  the  development 
of  an  abnormal  number  of  vertebrae  or  ribs,  are  not  un- 
common. .An  interesting  example  of  this  type  of  varia- 
tion is  found  in  the  development  of  extra  mammae. 
Supernumerary  nipples  in  mammals  are  a  common  form 
of  variation  among  humans.  Bruce1  found  fourteen 
cases  of  extra  mammae  among  2311  females  examined. 
Most  male  mammals  are  supplied  with  rudimentary 
nipples,  and  curiously  there  seems  a  greater  amount  of 
variation  among  males  than  females.  The  same  authority 
quoted  above  found  forty-seven  cases  of  multiple  nipples 
among  1645  males  examined.  In  one  case  a  woman 2 
is  reported  to  have  possessed  five  pairs  of  nipples.  The 
presence  of  a  larger  number  of  mammae  than  the  normal 
has  been  regarded  by  some  as  evidence  of  greater  fertility.3 
A  variation  in  the  opposite  direction  resulting  in  the 
development  of  a  smaller  number  of  digits  than  the  normal 

1  Bateson,  "Materials  for  the  Study  of  Variation." 

2  Ibid.,  p.  183. 

3  Bell,  "Multinippled  Sheep." 


VARIATION  199 

is  to  be  found  in  the  case  of  the  "  mule-footed  "  hog.  In 
this  instance,  the  split  hoof  has  united  into  one  solid 
hoof  like  the  horse,  and  this  variation  is  strongly  inherited. 
Meristic  variations  are  often  transmitted  by  heredity. 

190.  Functional  variations.  —  In  our  discussion  of 
variation  up  to  this  point,  we  have  chiefly  concerned 
ourselves  with  such  changes  as  are  exhibited  in  the  form 
of  animals.  We  have  now  to  consider  those  important 
modifications  which  affect  the  performance  of  the  indi- 
vidual. An  animal  may  retain  the  same  form  as  the 
average  of  the  race  but  be  vastly  more  efficient  in  the 
performance  of  some  one  or  more  of  the  physiological 
functions.  This  type  of  variation  is  one  of  the  most 
important  to  the  animal-breeder.  The  value  of  many  of 
the  domestic  animals  depends  entirely  upon  their  func- 
tional development.  The  chief  advantage  possessed  by 
some  domesticated  animals  over  their  wild  progenitors 
is  due  to  their  higher  functional  efficiency.  This  is  illus- 
trated by  the  domestic  cow,  the  improved  breeds  of  wool 
sheep,  and  the  trotting  horse.  Such  differences  in  form 
between  the  wild  and  domestic  sorts  as  are  present  are 
chiefly  significant  as  indicating  the  correlation  which  exists 
between  function  and  form.  The  changed  form,  if  it  ex- 
ists, is  incidental  and  the  result  of  functional  influence. 

The  valuable  variation  which  the  breeder  has  em- 
phasized in  his  selection  has  been  the  ability  of  the  animal 
to  produce  economically  and  largely  some  valued  animal 
product.  The  breeder  did  not  in  the  beginning  consciously 
select  variations  in  form.  It  is  true,  however,  that  the 
efficient  performance  of  animals  is  to  a  certain  extent 
correlated  with  the  form,  and  it  follows,  therefore,  that 
we  may  within  certain  rather  narrow  limits  rely  upon 
the  external  form  as  an  indication  of  functional  efficiency. 


200  THE  BREEDING  OF  ANIMALS 

191.  Examples  of  functional  variation.  —  In  most  cases 
the  functional  variations  in  the  domestic  animals  which 
have  become  valuable  to  man  are  modifications  of  natural 
functions  possessed  by  all  Wild  animals  living  under  nat- 
ural conditions.     The    present   stage  of  development  in 
domestic  forms  is  due  to  artificial  selection  practiced  by 
man.     The  variations  which  have  been  desirable  have 
been  preserved  through  selection  and  a  gradual  improve- 
ment in  functional  efficiency  has  resulted.     These  varia- 
tions may  arise  through   sudden  mutations,   but  such 
marked  changes  in  function  are  probably  less  common 
than  similar  mutations  in  form.     Variations  in  the  func- 
tional activities  of  animals  are  of  great  economic  impor- 
tance to  the  breeder  of  domestic  animals.     It  is  important 
to  know  with  some  degree  of  definiteness  the  extent  of 
variation  in  function,  as  such  knowledge  will  give  some 
idea  of  the  probable  limits  of  improvement.    The  follow- 
ing examples  of  functional  variation  will   be  useful  in 
helping  to  determine   the  limitations  of  improvement. 
Such  examples  may  be  greatly  multiplied  by  search  of 
the  literature  of  the  subject. 

192.  Variation  in  fertility   of    animals.  —  It  is  well 
known  that  there  are  wide  differences  among  individual 
animals  and  among  races  or  breeds  in  their  ability  to 
produce   large    numbers    of   offspring.     The   quality    of 
fertility  is  one  of  great  practical  importance  and  is  readily 
transmitted  by  heredity.     Miles  1  has  recorded  the  case 
of  a  cow  belonging  to  a  French  farmer  which  produced 
nine  calves  at  three  births,  four  at  the  first,  three  at  the 
second,  and  two  at  the  third.2    A  Teeswater  ewe  belonging 
to  Edward  Eddison  produced  four  lambs  in  1772  when 

1  Miles,  "Stock  Breeding,"  p.  131. 

2  "British  Husbandry,"  vol.  II,  p.  438. 


VARIATION  201 

two  years  old ;  "  in  1773,  five ;  in  1774,  two ;  in  1775, 
five;  in  1776,  two;  and  in  1777,  two.  The  first  nine 
lambs  were  lambed  within  eleven  months." l  The 
Country  Gentleman  reports  the  case  of  a  sow  that 
produced  twenty-three  pigs  at  one  birth.  The  above 
examples  are  of  Unusual  cases  of  fertility  and  are  so  far 
above  the  average  fertility  of  the  respective  races  of 
animals  that  they  represent  a  marked  departure  from 
the  established  type.  Other  things  being  equal,  those 
races  of  domestic  animals  which  are  most  fertile  are  most 
profitable.  One  of  the  qualities  of  economic  importance 
which  commends  certain  breeds  to  the  practical  farmer 
is  the  quality  of  fertility.  This  is  especially  true  among 
swine  and  sheep. 

193.  Variation  in  the  milking  function.  —  The  milk- 
ing function  in  domesticated  animals  is  of  special  interest 
for  the  reason  that  it  is  probably  the  most  valuable  single 
functional  variation  in  the  domestic  animals.  The  im- 
provement of  the  domestic  cow  in  the  direction  of  greater 
functional  efficiency  in  the  production  of  milk  and  butter 
has  been  little  short  of  marvelous.  This  improvement 
has  not  only  resulted  in  developing  an  animal  with  a 
capacity  to  produce  enormous  quantities  of  milk,  but  the 
efficiency  of  the  cow  in  the  economic  utilization  of  food 
has  been  no  less  noteworthy.  The  highly  improved 
domestic  cow  is  able  to  utilize  the  raw  products  of  the 
farm,  consisting  of  grain,  hay  and  grass,  and  produce 
from  these  a  larger  amount  of  human  food  than  any  other 
domestic  animal.  The  high  efficiency  of  the  milk  cow 
as  compared  with  the  beef  steer  is  clearly  shown  by  the 
records  kept  at  the  Missouri  Experiment  Station.2  A 

1  Culley,  "Live  Stock,"  p.  123. 

2  Eckles,  "  Dairy  Cattle,"  p.  6. 


202  THE  BREEDING  OF  ANIMALS 

Holstein  Friesian  cow  produced  18,405  pounds  of  milk 
in  one  year.  This  year's  production  from  one  cow  con- 
tained 2218  pounds  of  dry  matter.  At  the  same  station, 
the  carcass  of  a  1250-pound  fat  steer  was  analyzed.  The 
steer  was  twenty-one  months  old  and  had  been  fed  gen- 
erously from  birth.  The  steer's  carcass  contained  548 
pounds  of  dry  matter,  or  a  little  less  than  one-fourth  the 
amount  of  dry  matter  produced  by  the  cow  in  one  year. 
The  dry  matter  recorded  for  the  steer  was  for  the  entire 
carcass  of  the  animal,  including  hide,  horns,  bones  and 
intestines.  The  actual  net  weight  of  the  dry  matter  of 
the  edible  portion  of  the  fat  animal  was  only  357  pounds. 
In  other  words,  the  Holstein  Friesian  cow  produced  six 
times  as  much  edible  human  food  in  twelve  months  as 
was  produced  by  the  fattening  and  growing  steer  in 
twenty-one  months.  In  the  case  just  cited,  it  is  true 
that  the  cow  was  far  above  the  average  in  efficiency  while 
the  steer  was  a  fair  representative  of  a  good  average  beef 
animal.  The  example  is  nevertheless  a  most  excellent  il- 
lustration of  the  very  great  development  and  improvement 
of  the  dairy  cow  in  the  direction  of  desirable  variations. 
The  foregoing  records  of  the  two  animals  did  not  include 
the  dry  matter  consumed  in  the  production  of  milk  and 
beef.  Such  a  record  which  would  give  the  amount  of 
dry  matter  required  to  produce  a  pound  of  dry  matter  in 
milk  as  compared  with  a  pound  of  dry  matter  in  beef 
would  be  of  great  interest.  Such  records  have  been  kept 
at  a  number  of  American  experiment  stations. 

The  feed  and  milk  record  of  Pedro's  Ramaposa  181,160 
has  been  given  by  Eckles,1  and  from  this  the  dry  matter 
in  feed  which  is  required  to  produce  a  pound  of  dry  matter 

1  Eckles,  Missouri  Experiment  Station,  Research  Bulletin,  No. 
2,  p.  117. 


VARIATION  203 

in  milk  can  easily  be  determined.  The  cow,  Pedro's 
Ramaposa,  during  a  period  of  one  year  produced  8522.9 
pounds  of  milk  which  contained  1317  pounds  of  dry 
matter.  In  the  production  of  this  quantity  of  milk  she 
consumed  in  feed  9362  pounds  of  dry  matter.  In  other 
words,  the  consumption  of  100  pounds  of  dry  matter 
in  the  feed  resulted  in  the  production  of  91.12  pounds  of 
milk  containing  14.06  pounds  of  dry  matter.  Stated 
in  other  terms,  the  cow  here  described  produced  one  pound 
of  dry  matter  in  the  milk  for  each  7.1  pounds  of  dry 
matter  consumed  in  the  feed.  i 

194.  Variations  among  different  cows.  —  The  milking 
function  is  hereditary  and  is  a  comparatively  well-fixed 
character  among  the  dairy  breeds  of  cattle.  It  is  true, 
however,  that  there  still  exist  wide  variations  in  the 
productive  capacity  of  cows,  even  of  the  same  breeding 
as  well  as  those  of  different  ancestry.  The  Illinois 
Experiment  Station  1  in  several  tests  has  clearly  demon- 
strated the  wide  differences  which  may  exist  between 
individuals.2  Two  native  cows,  Rose,  nine  years  old, 
and  Nora,  six  years  old,  were  fed  the  same  kind  of 
a  ration  for  twelve  months.  The  amount  fed  was  de- 
termined by  the  appetites  of  the  animals.  The  table 
on  the  following  page  gives  the  essential  facts  of  interest 
in  this  connection. 

"  Reduced  to  a  like  feed  basis,  for  every  100  Ib.  of  milk 
given  by  Nora,  Rose  gave  139.5  Ib.,  and  for  every 
100  Ib.  of  butter-fat  produced  by  Nora,  Rose  produced 
180.7  Ib." 

Commenting  on  this  test,  Fraser  says,3  "  As  milk  is 

1  Fraser,  Illinois  Experiment  Station,  Bulletins  51  and  66. 

2  Davenport,  "Principles  of  Breeding,"  p.  78. 

3  Loc.  cit. 


204 


THE  BREEDING   OF  ANIMALS 


nearly  always  valued  by  the  amount  of  butter-fat  which 
it  contains,  and  Rose  produced  on  the  same  feed  basis 
1.807  times  as  much  butter-fat  as  Nora,  the  difference  in 
yield  between  the  two  cows  was  252.27  Ib.  of  butter-fat 
or  294.31  Ib.  of  butter  per  year.  This  at  16  cents  per 
pound,  which  is  the  average  value  of  butter  before  being 
made  up,  would  amount  to  $47.09  per  year.  Supposing 
that  the  cows  would  yield  in  this  ratio  for  six  years, 
from  the  age  of  four  to  ten,  which  is  a  conservative 
estimate,  Rose  would  produce  $282.54  worth  of  butter 
more  than  Nora  on  exactly  the  same  kind  and  quantity 
of  feed : 


RECORD  OP  THE   Two    Cows  FOR   ONE   YEAR   COMPUTED   ON 
A  LIKE  FEED  BASIS 


ROSE 

NOKA 

DIFFERENCE 

Reduced  to  a  like  feed  basis  the 
amount  Nora  would  have  pro- 
duced had  she  eaten  the  same 
as  Rose  : 

Total  digestible  dry  matter  con- 
sumed in  pounds 

6477  92 

6477  92 

Total  yield  of  milk,  in  pounds  . 
Total    yield    of    butter-fat,    in 
pounds 

11,329.00 
56480 

8121J60 
312  53 

3207.40 
25227 

Total  yield  of  butter,  in  pounds 
Total  value  of  butter  at  16jif  per 
pound.     .     .     ,     

658.90 
$  105.43 

364.62 

$58.34 

294.28 
$47.09 

"  In  this  comparison  Rose  was  at  a  disadvantage  in 
two  ways.  She  was  nine  years  of  age  and  on  the  down 
grade  of  life  while  Nora  was  just  in  her  prime.  Rose  was 
bred  November  5,  1899,  while  Nora  was  not  bred  until 


VARIATION  205 

after  the  experiment  closed.  Had  it  not  been  for  these 
two  hindrances  Rose  would  doubtless  have  made  even  a 
better  record  than  she  did. 

"  While  there  is  a  vast  difference  in  the  profit  derived 
from  the  two  cows  in  this  experiment,  the  difference  is 
by  no  means  phenomenal,  as  greater  differences  than 
here  cited  may  frequently  be  found  among  cows  in  the 
same  herd,  for  the  cow  Nora,  the  poorer  of  the  two,  was 
in  reality  an  exceptionally  good  cow,  producing  348  Ib. 
of  butter  in  a  year  which  is  nearly  three  times  the  average 
yield  (130  Ib.)  of  cows  in  the  United  States  and  almost 
one-half  more  than  the  average  yield  (250  Ib.)  of  profitable 
cows  in  Illinois.  Had  Rose  been  compared  with  a  really 
poor  cow,  such  as  may  be  found  in  nearly  all  dairy  herds, 
there  would  have  been  a  much  greater  difference  in  profit 
in  favor  of  Rose ;  for  she  gave  nearly  five  times  as  much 
as  a  profitable  cow  for  Illinois." 

In  the  cases  of  variation  mentioned,  the  individuals 
compared  have  belonged  to  different  breeds  or  have  been 
unrelated.  It  is  also  true  that  animals  which  are  from 
parents  of  the  same  blood  lines  may  show  wide  variations. 
In  the  dairy  herd  belonging  to  the  University  of  Missouri, 
there  were  at  one  time  nineteen  daughters  of  the  Jersey 
bull  Minette's  Pedro.  Many  of  the  mothers  of  these 
cows  were  from  another  bull  and  all  were  of  similar  breed- 
ing. The  conditions  surrounding  these  cows  were  alike ; 
their  dams,  grand  dams,  and  great  grand  dams  were  all 
similarly  bred  and  every  cow  of  the  nineteen  was  sired 
by  Minette's  Pedro.  These  cows  should  have  exhibited 
some  uniformity  in  the  development  of  dairy  qualities. 
The  table  records  the  annual  production  of  milk  and 
butter,  and  shows  rather  wide  variations  in  the  productive 
capacity  of  the  different  cows : 


206  THE   BREEDING   OF   ANIMALS 

RECORDS  OF  THE  DAUGHTERS  OP  MINETTE'S  PEDRO 


NUMBER 
LACTATION 
PERIODS 

AVERAGE 
LBS.  MILK 

AVERAGE 
LBS.  FAT 

Pedro's  Ramaposa  .  .  . 
Pedro's  Elf 

3 
3 

6750 
2225 

365.8 

109.4 

Pedro's  Alphea  Elf     ... 
University  May     .... 
Columbia  Huguita     .     .     . 
Pedro's  Daisy  Bate    . 
Missouri  Daizie     .... 
University  Daizie  .... 
University  Stella  .... 
University  Elf 

5 
3 
5 
2 
1 
4 
3 
4 

6151 
4723 
6322 
3456 
4910 
7746 
5336 
5053 

309.8 
227.0 
273.1 
193.7 
205.5 
405.6 
273.7 
247.3 

University  Belle  .... 
Pedro's  Grace  Briggs  .  . 
Pedro's  Matron  .... 
Iv^iss  IVtissouri 

3 
3 
3 
3 

4960 
4909 
6582 
6844 

223.8 
287.9 
355.9 
331  0 

Pedro's  Emily  Harris  .  . 
Pedro's  Estella  
Pedro's  Alphea  Ward  .  . 
Pedro's  May  Hubbard  .  . 
Pedro's  Virginia  Meredith  . 

3 
2 

1 
4 
3 

5271 

8807 
4728 
4073 
5776 

238.5 
462.1 
267.0 
184.9 
320.6 

195.  New  characters  originate  in  the  germ-plasm.  — 
In  the  preceding  discussion  of  the  possibility  of  the 
inheritance  of  acquired  characters,  we  have  followed 
closely  Weismann's  definition  of  acquired  characters.  It 
must  be  admitted,  however,  that  in  the  discussion  of 
this  subject  by  many  students  of  heredity,  the  use  of 
the  term  has  not  been  confined  strictly  to  Weismann's 
interpretation.  Many  biologists  would  include  under 
the  discussion  of  this  subject  all  acquired  characters, 
regardless  of  whether  they  may  have  originated  through 


1  Eckles,   Missouri   Experiment   Station,    Research   Bulletin, 
No.  2,  p.  108. 


VARIATION  207 

environmental  influences  acting  upon  the  soma-cells  or 
from  variations  directly  affecting  the  germ-plasm  itself. 

Many  new  characters  appearing  in  plants  and  animals 
cannot  be  traced  to  environmental  influences  acting  upon 
the  soma-cells.  Many  characters  seem  to  arise  inde- 
pendently of  external  causes.  They  undoubtedly  have 
their  origin  in  the  germ-plasm  itself.  Such  variations 
are  fundamentally  different  from  the  characters  which 
are  acquired  by  the  soma-cells  as  the  result  of  environment, 
use  or  disuse,  disease  and  mutilations. 

The  germ-cell  which  contains  within  its  own  substance 
the  materials  needed  for  giving  direction  to  the  develop- 
ment of  the  new  individual  is  the  result  of  the  union  of 
two  other  germ-cells  from  individuals  which  may  repre- 
sent widely  different  characters.  It  is  impossible  that 
the  new  individual  arising  from  such  a  germ-cell  shall 
possess  characters  identical  with  either  parent.  The 
offspring  represents  a  certain  amount  of  variation  which 
had  its  origin  in  the  germ-cell  itself. 

The  mechanism  of  reproduction,  including  the  matura- 
tion and  reduction  of  the  germ-cells  and  the  union  of  the 
chromosomes,  provides  ample  opportunity  for  new  com- 
binations of  characters  which  may  profoundly  change 
the  whole  physiological  history  of  the  offspring. 

196.  Mutilations.  —  Many  examples  of  mutilations 
and  their  supposed  transmission  from  parent  to  offspring 
have  given  to  advocates  of  the  belief  in  the  transmission 
of  acquired  characters  many  of  their  most  interesting 
examples.  Various  investigators  have  cut  off  the  tails 
of  mice  for  many  generations  with  a  view  to  investigating 
the  result  of  such  mutilation  upon  its  transmissibility. 
Cope,  Mantegazza  and  Rosenthal  cut  off  the  tails  of  mice 
for  eleven  generations,  Bos  for  fifteen,  and  Weismann 


208  THE  BREEDING  OF  ANIMALS 

for  nineteen  generations,  but  in  no  single  case  was  there 
the  slightest  evidence  that  this  form  of  mutilation  was 
transmitted. 

The  tails  of  sheep  have  been  cut  off  for  many  hundred 
years  by  shepherds,  but  tails  reappear  regularly  with  the 
normal  number  of  vertebrae  and  without  diminution  in 
length. 

A  large  number  of  examples  have  been  given  of  cats 
whose  tails  have  been  removed  and  who  have  later  trans- 
mitted to  their  offspring  a  tendency  to  short  tails.  In 
the  Eiffel,  the  peasants  shorten  the  tails  of  cats.  It  is 
reported  by  Tietz  that  cats  with  defective  tails  are  common 
in  this  region.  Many  similar  examples  are  reported.  In 
this  and  most  other  examples  of  the  inheritance  of  acquired 
characters,  there  is  no  evidence  that  the  artificial  shorten- 
ing of  the  tails  is  the  direct  cause  of  the  atrophied  tails 
observed  in  the  kittens.  Such  defective  tails  are  not 
uncommon  in  races  of  cats  with  normal  tails.  It  must 
also  be  remembered  that  there  are  tailless  breeds  of  cats 
such  as  the  Manx  and  Japanese  breeds,  and  the  admixture 
of  such  breeds  might  be  sufficient  to  explain  the  observed 
variations. 

The  cattlemen  of  the  Nile  Valley  have  for  an  unknown 
period  of  time  caused  the  horns  of  cattle  to  grow  in  curi- 
ous spiral  forms,  but  there  is  no  evidence  that  such 
deformities  are  transmitted  to  the  offspring.1 

197.  The  Brown-Sequard  experiments.2  —  The  most 
frequently  quoted  and  credible  scientific  experiment 
conducted  for  the  purpose  of  causing  somatic  modifica- 
tions and  observing  their  transmission  from  parent  to 

1  Hartman,    "Die   Haussaugethiere   der   Wildlander,"    Ann. 
Landivirthsch.,  Berlin,  1864,  p.  28. 

2  Romanes,  "Darwin  and  after  Darwin,"  vol.  II,  chap.  IV. 


VARIATION  209 

offspring  are  the  famous  Brown-Sequard  experiments 
with  guinea  pigs.  From  1869  to  1891,  Brown-Sequard 
cut  the  sciatic  nerve  of  the  leg  or  the  spinal  cord  in  the 
dorsal  region,  causing  an  abnormal  nervous"  condition 
resembling  the  symptoms  of  epilepsy.  These  animals  when 
allowed  to  breed  produced  offspring,  many  of  which  were 
epileptic  like  the  parents.  Similar  results  were  later 
secured  by  Westphal,  Dupuy,  Obersteiner  and  Romanes. 
This  interesting  investigation  has  been  promptly  accepted 
by  the  special  advocates  of  the  transmission  of  acquired 
characters  as  fulfilling  the  oft  repeated  demand  for  direct 
evidence  of  the  inheritance  of  somatic  modifications. 

In  discussing  the  results  it  must  not  be  forgotten  that 
the  mutilation  was  never  transmitted,  but  only  the  epilep- 
tic state  resulting  from  the  mutilation.  The  results  from 
this  type  of  mutilation  were  very  diverse.  According  to 
Romanes,  the  epileptic  condition  was  rarely  transmitted. 
Brown-Sequard  admitted  that  certain  particular  results 
were  exhibited  in  only  one  or  two  per  cent  of  cases.  If 
this  mutilation  had  actually  influenced  the  germ-plasm 
in  such  a  way  as  to  add  to  its  fundamental  constitution 
the  determiners  essential  for  the  development  of  the  new 
characters,  then  surely  we  might  expect  a  larger  part  of 
the  offspring  to  be  affected  with  the  acquired  character. 

Max  Sommer  in  1900  repeated  the  Brown-Sequard 
experiments,  but  failed  to  confirm  the  conclusion  that 
this  experiment  had  proven  the  existence  of  acquired 
characters.  "  As  regards  the  hereditary  transmission  of 
epilepsy  in  guinea  pigs,"  says  Sommer,  "or  of  other 
accidentally  acquired  pathological  symptoms  —  e.g.  de- 
fects in  the  toes  —  we  have  not  been  able  to  confirm 
the  experiments  of  Brown-Sequard  and  Obersteiner; 
and  we  do  not  think  that  these  can  any  longer  serve  as 


210  THE  BREEDING  OF  ANIMALS 

a  support  to  the  doctrine  of  the  inheritance  of  acquired 
characters/' 1 

198.  Causes  of  variation.  —  The  nature  of  variation 
is  still  obscure.     The  fundamental  causes  are  not  easily 
determined.     "  Our  ignorance  of  the  laws  of  variation 
is  profound,"  says  Darwin. 

The  results  of  the  investigations  in  cytology  have  given 
a  more  reasonable  basis  for  understanding  the  subject 
of  variation,  but  it  has  not  yet  given  us  a  wholly  satis- 
factory knowledge  of  the  causes  of  variation.  Bateson 
holds  that  we  are  yet  far  from  a  satisfactory  explanation 
of  the  real  nature  of  variation.  He  has  concluded  that 
"  Inquiry  into  the  causes  of  variation  is,  in  my  judgment, 
premature."  We  are,  however,  able  to  recognize  and 
classify  certain  apparent  causes  of  variation.  Such  clas- 
sification recognizes  causes  of  variation  as  external  and 
internal. 

Davenport 2  has  further  classified  the  internal  causes 
of  variation  as:  "  1.  Internal  influences  affecting  pri- 
marily the  individual,  and  2.  internal  influences  affecting 
the  race  as  a  whole." 

199.  Cell  division  a  cause  of  variation.  —  Every  animal 
is  the  product  of  the  union  of  the  germ  substance  of  two 
other  animals.     The  union  of  the  germ-cells  is  a  union 
of  the  characters  of  the  parents.     This  combination  of 
the  germinal  matter  of  the  two  parents  results  in  a  rear- 
rangement of  some  of  the  characters,  and  these  may  vary 
materially  from  the  original  characters  of  the  parents. 
Weismann  calls  this  mixing  of  the  germ-plasm  amphimixis. 
He  is  of  the  opinion  that  sexual  reproduction  by  cell  union 
and  cell  division  is  nature's  plan  for  increasing  variation. 

1  Thomson,  "  Heredity,"  pp.  230-236. 

2  Davenport,  "Principles  of  Breeding,"  p.  155. 


VARIATION  211 

New  characters  may  arise  or  old  ones  be  lost  through 
accidents  to  the  germ  substance  during  the  processes  of 
cell  division  incident  to  reproduction  and  growth.  It  is 
conceivable  that  a  chromosome  bearing  within  its  ma- 
terial substance  a  character  or  set  of  characters  may  be 
lost  or  destroyed  at  some  stage  of  the  complicated  pro- 
cesses which  eventually  result  in  the  formation  of  a  new 
germ-cell.  If  such  a  thing  occurs,  it  must  influence 
greatly  the  ultimate  characters  of  the  individual.  It  is 
also  apparent  that  a  fundamental  change  in  the  germinal 
material  may  influence  not  alone  the  resulting  individual 
but  the  race  or  breed.  Sudden  marked  variations  may 
and  do  often  occur,  and  these  may  become  the  beginnings 
of  new  races.  These  sudden  variations  are  called  muta- 
tions by  De  Vries,  and  the  mutation  theory  of  evolution 
is  regarded  as  one  of  the  most  important  advances  since 
Darwin.  A  fuller  discussion  of  mutations  will  be  found 
on  another  page. 

It  is  difficult  to  differentiate  between  those  variations 
which  are  merely  the  result  of  the  action  of  environment 
on  the  soma-  or  body-cells  and  those  variations  which 
are  the  result  of  a  fundamental  change  in  the  constitu- 
tion of  the  germ  substance.  The  former  are  generally 
temporary  and  affect  only  the  individual,  but  do  not 
influence  the  germ  sufficiently  to  cause  the  same  varia- 
tion to  appear  in  the  offspring.  The  highly  improved 
types  of  domestic  swine  if  permitted  to  run  wild  in  the 
woods  lose  their  rounded  full-fleshed  form  and  assume 
much  the  appearance  of  the  unimproved  "  razor-back." 
Their  appearance  is  so  changed  by  this  treatment  that 
the  most  skillful  judge  of  swine  would  be  greatly  deceived. 
The  "  razor-back,"  on  the  other  hand,  has  subsisted  for 
generations  upon  the  mast  of  the  forest.  This  has  in- 


212  THE  BREEDING  OF'  ANIMALS 

volved  much  exercise  and  the  ability  to  live  on  a  scant 
supply  of  food  at  certain  seasons.  These  conditions  have 
resulted  in  changing  the  form  of  the  body.  The  neck 
and  jaws  are  larger  and  well  muscled.  The  back  is  sharp, 
legs  longer  and  ribs  flatter  than  in  the  improved  forms. 
If  the  young  pigs  of  these  unimproved  swine  are  placed 
under  conditions  where  they  are  supplied  with  an  abun- 
dance of  nutritious  food,  they  approach  somewhat  the  well- 
rounded  form  of  the  improved  type.  In  each  of  these 
cases  the  environment  has  resulted  in  causing  a  distinct 
variation  from  the  parent  form.  This  variation  can  be 
easily  observed,  it  can  be  measured.  But  whether  this 
environment  has  influenced  in  any  way  or  how  much  it 
has  influenced  the  elemental  carriers  of  heredity  in  the 
germ,  it  is  impossible  to  do  more  than  conjecture.  It 
cannot  be  accurately  measured.  Biologists  are  generally 
agreed  that  in  a  case  of  this  kind  the  germ  is  not  funda- 
mentally changed. 

200.  Influence  of  use  and  disuse  in  causing  modifica- 
tions. —  The  constant  use  of  an  organ  in  the  performance 
of  work  will  modify  the  organ  in  accordance  with  the  work 
performed.  Any  organ  of  the  body  that  is  not  used  may 
atrophy.  Changes  resulting  from  excessive  use  of  the 
various  parts  of  the  body  may  be  so  extensive  as  to  appear 
almost  as  new  characters.  If  modifications  resulting 
from  food,  climate  or  mutilations  are  transmitted,  the 
changes  resulting  from  the  constant  use  of  an  organ  should 
be  transmitted  with  equal  or  greater  force. 

Lamarck's  theory  of  evolution  was  largely  based  upon 
the  supposed  adaptation  of  the  various  organs  of  the 
body  to  their  environment,  and  that  such  adaptations 
were  readily  transmitted.  Thus  the  giraffe,  forced  by 
conditions  to  feed  upon  the  leaves  of  trees,  gradually 


VARIATION  213 

extended  his  neck,  which  became  longer,  and  this  increase 
in  length  was  transmitted  from  generation  to  generation. 
Wading  birds,  feeding  in  the  shallow  water  along  the  shore, 
gradually  waded  deeper  and  deeper  into  the  water. 
Their  legs  became  longer,  and  the  additional  length  gained 
by  each  generation  was  transmitted.  The  long  tongue 
of  the  ant-eater,  of  woodpeckers,  and  humming  birds, 
was  developed  in  a  similar  manner.  The  rudimentary 
eyes  of  subterranean  animals  and  fish  in  caves  is  another 
supposed  example  of  the  loss  of  an  organ  through  disuse. 

Among  domestic  animals,  there  are  numerous  examples 
of  a  high  degree  of  development  of  organs  through  con- 
tinued exercise.  The  milking  function  in  the  dairy  cow 
can  undoubtedly  be  greatly  improved  in  any  individual 
by  skillful  exercise  and  use.  The  training  of  running  and 
trotting  horses  has  resulted  in  very  greatly  increasing 
the  ability  of  an  animal  in  those  particular  types  of  speed. 
Are  these  modifications,  the  result  of  use  or  disuse,  trans- 
mitted by  heredity?  Such  inheritance  would  be  of  the 
very  greatest  importance  to  the .  breeder  of  domestic 
animals.  In  answer  to  this  question  no  direct  proof  has 
been  offered  that  characters  acquired  by  exercise  or  lost 
by  disuse  are  actually  transmitted  by  heredity. 

201.  Importance  of  causes  of  variation  to  the  breeder 
of  domestic  animals.  —  While  the  researches  of  biologists 
have  led  them  to  believe  that  the  germ-plasm  is  very 
stable  and  its  character  not  easily  changed  by  the  environ- 
ment of  the  body,  it  is  nevertheless  true  that  breeders  of 
the  domestic  animals  have  long  believed  that  the  amount 
and  kind  of  food,  climate  and  training  which  animals 
receive  has  an  influence  not  only  upon  the  individuals 
benefiting  by  or  suffering  from  such  environment,  but 
likewise  may  have  a  profound  influence  upon  their  pos- 


214  THE  BREEDING  OF  ANIMALS 

terity.  The  breeder  of  beef  cattle  believes  that  the  off- 
spring of  parents  which  are  kept  in  good  or  even  in  fat 
condition  are  more  apt  to  possess  a  tendency  to  fatten 
readily  than  the  offspring  of  parents  kept  in  very  thin 
condition.  The  breeder  of  trotting  horses  prefers  to  use 
in  his  stud  a  stallion  that  has  a  record  and  mares  that 
have  benefited  from  severe  training. 

In  this  case  the  biologist  is  probably  in  the  main  cor- 
rect in  his  conclusions  from  the  standpoint  of  inheritance. 
But  it  is  also  true  that  the  breeder  of  beef  cattle  is  right 
in  maintaining  his  beef  animals  on  a  high  plane  of  nutri- 
tion, not  because  this  will  materially  affect  the  germ-plasm, 
but  because  such  treatment  gives  the  breeder  an  accurate 
measure  of  the  beef-producing  characters  of  his  breeding 
animals.  How  can  the  breeder  know  that  a  particular 
bull  or  cow  possesses  the  ability  to  lay  on  fat  rapidly 
unless  he  actually  tests  the  animal  ?  The  breeder  of 
trotting  horses  likewise  cannot  judge  accurately  from  an 
external  examination  of  a  horse  how  fast  he  can  trot.  He 
must  be  trained  and  his  full  speed  developed. 

Such  treatment  on  the  part  of  the  breeder  is  not  for 
the  purpose  of  changing  the  hereditary  capacities  of  an 
animal,  but  for  the  purpose  of  aiding  selection.  Animals 
so  treated  that  do  not  come  up  to  the  standard  set  by  the 
breeder  are  eliminated.  The  desirable  animals  are  pre- 
served and  encouraged  to  reproduce. 

202.  Germinal  variations.  —  The  term  variation  has 
suffered  from  careless  use,  and  such  use  has  led  to  some 
confusion  of  ideas.  Differences  appearing  in  the  offspring 
may  be  due  to  variations  in  the  germ,  or  they  may  be  due 
to  the  influence  of  environment.  What  the  animal 
actually  is  depends  upon  the  constitution  of  the  germ. 
The  offspring  may  be  exactly  like  the  parent  in  the  con- 


VARIATION  215 

stitution  of  the  germ  substance  from  which  each  has 
been  developed,  but  they  may  appear  to  be  different. 
Such  differences  may  be  due  to  a  change  in  the  environ- 
ment which,  acting  upon  the  organism,  may  have  modified 
the  apparent  character  of  the  individual.  Such  changes 
are  not  variations  in  the  true  sense,  but  rather  modifica- 
tions. It  is  not  always  possible  to  distinguish  readily 
between  changes  which  are  merely  modifications  and 
variations  which  are  due  to  fundamental  changes  in  the 
germ.  To  the  practical  breeder,  it  is  in  the  highest 
degree  important  that  this  distinction  between  mere 
modifications  due  to  environment  and  germinal  varia- 
tions due  to  a  change  in  the  constitution  of  the  germinal 
substance  be  clearly  recognized..  The  latter  variations 
are  strongly  transmitted  by  heredity;  the  former  are 
not  transmissible.  Domestic  animals  kept  under  the 
same  conditions  often  exhibit  wide  variations,  and  these 
are  often  germinal  and  consequently  inherited.  Those 
variations  or,  more  properly,  modifications  which  appear 
in  individuals  and  are  the  result  of  environment  are  of 
little  significance  to  the  breeder.  If  the  breeder  of  speed 
horses  confined  his  selection  solely  to  those  horses  that 
had  been  trained,  he  might  not  secure  the  sum  total  of 
those  characters  in  the  fundamental  constitution  of  the 
animal  which  represent  the  highest  capacity  for  speed. 
It  is  true  that  among  horses  of  similar  ancestry  the  train- 
ing and  development  is  the  most  accurate  index  of  the 
capacities  which  they  have  inherited.  But  a  horse 
that  has  not  been  trained  and  hence  modified  by  environ- 
ment may  actually  possess  through  inheritance  a  greater 
capacity  for  speed.  The  latter  horse  may  show  less 
speed  than  the  horse  that  has  been  carefully  developed, 
but  he  will  be  a  better  breeder.  Let  us  assume  for  example 


216  THE  BREEDING  OF  ANIMALS 

that  we  have  two  horses  under  consideration,  of  the  same 
ancestry.  One  horse  has  through  germinal  variation 
been  endowed  with  an  ability  to  trot  or  run  at  a  certain 
speed  without  training.  The  other  horse  cannot  attain 
the  same  speed  except  as  the  result  of  long  and  careful 
training.  They  have  attained  the  same  rate  of  speed, 
but  one  has  acquired  this  speed  through  the  influence 
of  environment  and  this  increased  speed  becomes,  there- 
fore, a  mere  modification.  The  other  horse  owes  his 
ability  to  go  fast  to  a  variation  in  the  fundamental  con- 
stitution of  the  germ  substance.  The  latter  horse  will 
be  the  better  breeder  because  germinal  variations  are 
transmitted,  and  modifications  which  result  from  the 
influence  of  environment  are  apparently  not  transmitted. 


CHAPTER  XI 
IN-BREEDING 

THE  breeder  of  domestic  animals  is  frequently  confronted 
with  the  problem  of  in-breeding.  If  in-breeding  is  not 
followed  by  injury,  it  would  often  be  a  convenient  method 
of  improvement.  The  value  of  a  proven  and  tested  sire 
is  so  great  that  if  he  could  be  safely  mated  with  his  own 
offspring  it  would  be  of  great  economic  advantage  to 
the  breeder.  If,  on  the  other  hand,  positive  advantages 
follow  the  mating  of  closely  related  animals,  the  breeder 
should  know  what  these  advantages  are  and  how  and  when 
they  may  be  most  certainly  realized. 

203.  Definitions.  —  In-breeding  has  been  variously 
designated  as  close-breeding,  consanguineous  breeding, 
in-and-in-breeding,  inter-breeding  and  incestuous  breed- 
ing. The  term  in-breeding  is  used  to  indicate  the  mating 
of  animals  which  are  near  of  kin  or  closely  related.  The 
degree  of  relationship  which  it  is  proper  to 'designate 
as  in-breeding  is  a  matter  of  some  disagreement.  •  Stone- 
henge,  for  example,  has  defined  in-breeding  as  "  The 
pairing  of  relations  within  the  degree  of  second  cousins, 
twice  or  more  in  succession."  Randall  would  restrict 
the  application  of  the  term  to  "  animals  of  precisely  the 
same  blood  as  own  brother  and  sister." 

It  would  be  very  desirable  if  the  term  "  in-breeding  " 
could  be  limited  in  its  application  as  suggested  by  Mor- 

217 


218  THE   BREEDING  OF  ANIMALS 

gan.1  "  For  species  with  separate  sexes  the  term  '  in- 
breeding '  is  used  to  express  either  the  union  between 
brothers  and  sisters  or  between  offspring  and  parent,  in 
one  or  more  generations/'  Unfortunately  the  literature 
on  the  subject  of  in-breeding  has  not  placed  such  narrow 
limitations  on  the  term. 

It  must  be  recognized  that  there  are  different  degrees 
of  in-breeding.  Animals  may  be  closely  in-bred  as,  for 
example,  results  from  the  mating  of  parent  and  offspring, 
or  brother  and  sister.  The  union  of  more  distant  rela- 
tionships, as  third  or  fourth  cousins,  would  not  be  expected 
to  show  the  same  good  or  bad  results  in  the  offspring  as 
the  more  closely  related  parents.  In  the  literature  of 
the  subject,  the  discussions  generally  have  reference  to 
the  most  intensive  forms  of  close-breeding.  The  results, 
good  or  bad,  therefore,  are  those  which  may  be  expected 
to  follow  the  most  intensive  in-breeding.  After  all,  the 
real  question  of  importance  for  the  practical  breeder  to 
answer  is  not  whether  any  form  of  in-breeding  should 
be  practiced,  but  to  what  extent  it  may  be  practiced  and 
its  known  advantages  become  realized.  In  a  sense,  prac- 
tically every  registered  improved  breed  to-day  is  the 
result  of  a  certain  amount  of  in-breeding.  David  Starr 
Jordan  has  calculated  that  if  no  in-breeding  of  any  degree 
had  taken  place  in  the  human  race,  each  person  born 
in  the  thirtieth  generation  from  William  the  Conqueror 
would  have  had  8,598,094,592  living  ancestors  at  the 
time  when  the  Conqueror  was  alive. 

204.  Advantages  claimed  for  in-breeding.  —  The  mat- 
ing of  animals  having  the  same  parentage,  has  resulted 
in  certain  definite  advantages  to  the  race  or  breed.  These 
results  are  as  easily  demonstrable  as  are  the  results  from 

1  Morgan,  "  Experimental  Zoology,"  1907,  p.  186. 


IN-BREEDING  219 

any  other  system  or  method  of  breeding.  The  particular 
beneficial  result  most  commonly  claimed  is  that  in-breed- 
ing is  the  quickest  method  of  fixing  and  perpetuating  a 
desirable  character.  Closely  related  animals  are  most 
likely  to  possess  the  character  sought,  and  mating  animals 
having  the  qualities  which  the  breeder  particularly  desires 
to  perpetuate  in  the  breed  is  the  most  natural  method 
of  accomplishing  his  purpose.  In-breeding  tends  to  in- 
tensify the  good  qualities  which  the  breeder  is  striving 
to  make  dominant.  It  does  not  cause  new  and  desirable 
characters  to  appear,  but  is  merely  a  method  of  making 
the  greatest  possible  use  of  such  characters. 

Thus  in-bred  animals  are  strongly  prepotent.  They 
possess  to  an  unusual  degree  the  power  of  fixing  their 
qualities  upon  their  offspring.  This  is  manifestly  the 
most  important  characteristic  in  a  highly  improved  breed- 
ing animal.  Next  to  the  possession  of  the  highly  improved 
characters  which  make  the  domestic  animals  useful  to 
man,  their  ability  to  transmit  those  qualities  is  most 
important.  In-breeding  is  one  certain  means  of  develop- 
ing the  prepotency  of  animals. 

It  is  a  fundamental  principle  of  breeding  that  the 
smaller  the  number  of  qualities  selected  for  improvement 
by  the  breeder,  the  more  rapid  and  certain  will  be  his 
progress  in  the  improvement  of  the  breed.  In- 
breeding tends  to  reduce  the  number  of  characters,  sim- 
plify the  breeding  operations,  and  thus  makes  more 
certain  the  continued  reappearance  of  the  valuable 
characters  in  succeeding  generations. 

205.  Bad  results  from  in-breeding.  —  In  recounting 
the  well-known  benefits  which  follow  intelligent  in-breed- 
ing, it  is  not  intended  to  convey  the  impression  that 
in-breeding  results  only  in  success.  The  biological  pro- 


220  THE   BREEDING   OF  ANIMALS 

cesses  which  result  in  simplifying  the  germ-plasm  and 
intensifying  the  powers  of  transmission  act  impartially 
on  all  characters  alike,  bad  as  well  as  good.  Lurking 
tendencies  to  evil  may  become  strengthened  along  with 
the  good,  and  thus  be  more  strongly  transmitted  than 
before. 

Such  a  result  cannot  always  be  foreseen  and  hence 
when  breeding  closely  related  animals,  there  is  always 
the  risk  that  we  will  produce  offspring  which  are  not  only 
more  prepotent  in  respect  to  the  good  qualities  we  are 
seeking  to  develop  and  perpetuate,  but  we  may  at  the 
same  time  bring  about  the  same  result  in  connection  with 
the  bad  qualities. 

But  aside  from  the  bad  results  following  in-breeding 
which  may  be  ascribed  to  the  simplifying  of  the  germ- 
plasm  and  the  intensifying  of  the  tendencies  to  evil,  it 
has  long  been  held  by  many  eminent  biologists  and  by 
practical  breeders  that  certain  definite  evil  results  always 
follow  long-continued  in-breeding.  The  most  important 
of  these  necessary  evils  are  loss  of  vigor,  decreased  fer- 
tility and  diminished  size. 

206.  Decreased  fertility  and  vigor  from  in-breeding.  — 
Many  breeders  believe  that  continuous  in-breeding  results 
in  a  loss  of  fertility.  It  is  admitted  that  most  other 
qualities  may  be  advantageously  improved  by  close- 
breeding,  but  that  the  quality  of  fertility  is  an  exception. 
This  belief  is  firmly  implanted  in  the  minds  of  the  greater 
number  of  breeders  and  of  many  biologists.  The  basis 
for  such  a  belief  is  found  in  the  results  of  certain  specific 
investigations  and  the  general  experience  of  breeders. 
Fertility  is  a  character  of  prime  importance  in  the  domestic 
animals.  This  character  is  undoubtedly  subject  to  the 
same  general  laws  of  transmission  as  are  all  other  hered- 


IN-BREEDING  221 

itary  qualities.  We  have  seen  how  in-breeding  may  be 
used  to  intensify  and  fix  the  other  desirable  characters 
of  a  breed,  and  incidentally  greatly  increase  their  pre- 
potency. If  an  animal  is  possessed  of  the  quality  of 
fertility  to  an  unusual  degree,  why  may  not  in-breeding 
be  employed  to  increase  fertility  as  well  as  to  improve 
the  qualities  of  speed  in  horses  or  of  early  maturity 
in  meat-producing  animals  ?  Let  us  answer  the  question 
by  an  examination  of  the  available  data.  Is  in-breeding 
per  se  specifically  injurious  to  the  fertility  of  plants  and 
animals?  If  in-breeding  is  injurious  at  all,  how  serious 
is  the  injury  and  how  far  can  the  breeder  take  advantage 
of  the  known  good  results  without  sacrificing  the  impor- 
tant quality  of  fertility  ?  The  data  available  for  answer- 
ing these  questions  are  to  be  found  in  the  practical  experi- 
ence of  breeders  and  the  results  from  carefully  planned 
experiments  where  all  other  factors  have  been  eliminated 
excepting  only  the  factor  of  in-breeding. 

207.  Darwin's  researches.  —  The  greatest  single  con- 
tribution to  the  subject  of  in-breeding  was  made  by  Dar- 
win. Recognizing  the  advantages  of  close  in-breeding 
in  fixing  desirable  characters  and  admitting  that  these 
advantages  may  outweigh  possible  injury,  he  brings 
forward  an  array  of  examples  of  the  injurious  effects  of 
in-breeding  which  are  convincing.  His  conclusions  are 
best  stated  in  his  own  words : 

1 "  That  any  evil  directly  follows  from  the  closest 
inter-breeding  has  been  denied  by  many  persons ;  but 
rarely  by  any  practical  breeder;  and  never,  as  far  as  I 
know,  by  one  who  has  largely  bred  animals  which  prop- 
agate their  kind  quickly.  Many  physiologists  attribute 

1  Darwin,  "Animals  and  Plants  under  Domestication,"  vol. 
II,  p.  94. 


222  THE   BREEDING   OF   ANIMALS 

the  evil  exclusively  to  the  combination  and  consequent 
increase  of  morbid  tendencies  common  to  both  parents; 
and  that  this  is  an  active  source  of  mischief  there  can  be 
no  doubt.  It  is  unfortunately  too  notorious  that  men 
and  various  domestic  animals  endowed  with  a  wretched 
constitution,  and  with  a  strong  hereditary  disposition 
to  disease,  if  not  actually  ill,  are  fully  capable  of  procre- 
ating their  kind.  Close  inter-breeding,  on  the  other  hand, 
often  induces  sterility ;  and  this  indicates  something  quite 
distinct  from  the  augmentation  of  morbid  tendencies 
common  to  both  parents.  The  evidence  immediately 
to  be  given  convinces  me  that  it  is  a  great  law  of  nature, 
that  all  organic  beings  profit  from  an  occasional  cross 
with  individuals  not  closely  related  to  them  in  blood ; 
and  that,  on  the  other  hand,  long-continued  close  inter- 
breeding is  injurious." 

Darwin's  conclusions  are  based  upon  a  very  large 
number  of  observations.  Experienced  breeders  who  are 
accurate  observers,  such  as  Sir  J.  Sebright,1  Andrew 
Knight  and  Herman  von  Nathusius,  all  agree  as  to  the 
certain  injury  which  always  follows  long-continued  in- 
breeding. 

Darwin's  investigations  led  him  to  believe  that  while 
many  species  of  plants  and  animals  are  hermaphroditic 
and  hence  self-fertilizing,  and  these  might  be  presumed 
perpetually  to  fertilize  themselves,  yet  he  failed  to  find 
a  single  species  in  which  nature  had  provided  structures 
which  insured  self-fertilization.  On  the  other  hand,  he 
found  innumerable  instances  in  which  nature  had  pro- 
vided special  structures  for  the  sole  apparent  purpose  of 
insuring  cross-fertilization  and  thus  preventing  perpetual 
in-breeding. 

1  Sebright,  "The  Art  of  Improving  the  Breed,"  1809. 


IN-BREEDING  223 

208.  In-breeding  cattle.  —  BakewelTs 1  (1725-1795) 
phenomenal  success  in  the  rapid  improvement  of  horses, 
cattle  and  sheep  was  possible  only  because  he  utilized 
to  the  fullest  extent  the  method  of  mating  animals  of 
the  closest  possible  relationship,  not  because  they  were 
closely  related  but  because  they  possessed  the  particular 
qualities  desired.  By  in-breeding  he  was  able  to  "  sim- 
plify "  the  germ-plasm  and  bring  about  a  homozygous 
condition  of  these  particular  characters.  The  available 
breeding  records  of  the  activities  of  Robert  and  Charles 
Colling,  Thomas  Bates  and  the  Booths  are  eloquent  in 
their  testimony  of  the  fact  that  great  progress  was  achieved 
from  intelligent  in-breeding. 

The  Shorthorn  bull,  Duke  of  Airdrie  (12,730),2  traces 
through  five  or  six  generations  to  but  six  animals  famous 
in  the  early  history  of  the  Shorthorn  breed.  The  six 
animals  all  trace  back  through  five  or  six  generations  to 
one  bull  Favourite,  himself  the  son  of  half-brother  and 
sister.  Says  Darwin,3  "  But  the  Shorthorns  offer  the 
most  striking  case  of  close  inter-breeding;  for  instance, 
the  famous  bull  Favourite  (who  was  himself  the  offspring 
of  a  half-brother  and  sister  from  Foljambe)  was  matched 
with  his  own  daughter,  granddaughter,  and  great-grand- 
daughter; so  that  the  produce  of  this  last  union,  or  the 
great-great-granddaughter,  had  15-16ths,  or  93.75  per 
cent  of  the  blood  of  Favourite  in  her  veins.  This  cow 
was  matched  with  the  bull  Wellington,  having  62.5  per 
cent  of  Favourite  blood  in  his  veins,  and  produced  Cla- 
rissa ;  Clarissa  was  matched  with  the  bull  Lancaster,  hav- 

1Youatt,  "Cattle,"  p.  199. 

2  A  valuable  discussion  of  in-breeding  among  early  breeders 
is  to  be  found  in  Miles'  "Stock  Breeding,"  pp.  137-189.     Also 
Huth,  "The  Marriage  of  Near  Kin,"  pp.  242-292. 

3  Darwin,  "Animals  and  Plants  under  Domestication,"  p.  96. 


224  THE   BREEDING   OF  ANIMALS 

ing  68.75  of  the  same  blood,  and  she  yielded  valuable 
offspring.  Nevertheless  Collings,  who  reared  these  ani- 
mals, and  was  a  strong  advocate  for  close-breeding,  once 
crossed  his  stock  with  a  Galloway,  and  the  cows  from 
this  cross  realized  the  highest  prices.  Bates's  herd  was 
esteemed  the  most  celebrated  in  the  world.  For  thirteen 
years  he  bred  most  closely  in-and-in;  but  during  the 
next  seventeen  years,  though  he  had  the  most  exalted 
notion  of  the  value  of  his  own  stock,  he  thrice  infused 
fresh  blood  into  his  herd :  it  is  said  that  he  did  this,  not 
to  improve  the  form  of  his  animals,  but  on  account  of 
their  lessened  fertility." 

The  opinion  of  a  great  breeder  who  has  practiced 
very  close  in-breeding  for  eighty  years  and  who  has  also 
been  noted  for  the  general  success  of  his  breeding  opera- 
tions and  the  high  quality  of  his  cattle,  so  much  so  as  to 
have  been  called  one  of  the  founders  of  the  breed,  is  of 
great  interest  in  this  connection.  Such  a  breeder  was 
Price  of  England.  He  says,1  "  My  herd  of  cattle  has, 
therefore,  been  bred  in-and-in,  as  it  is  termed,  for  upward 
of  eighty  years,  and  by  far  the  greater  part  of  it  in  a  direct 
line,  on  both  sides,  from  one  cow  now  in  calf  for  the  twen- 
tieth time.  I  have  bred  three  calves  from  her,  by  two 
of  her  sons,  one  of  which  is  now  the  largest  cow  I  have, 
possessing  also  the  best  form  and  constitution ;  the  other 
two  were  bulls,  and  proved  of  great  value,  thus  showing 
indisputably  that  it  is  not  requisite  to  mix  the  blood  of 
the  different  kinds  of  the  same  race  of  animals,  in  order 
to  keep  them  from  degenerating." 

209.  The  Chillingham  cattle.  —  The  wild  white  cattle 
of  Great  Britain  are  believed  to  be  the  only  living  pure 
descendants  of  the  original  wild  cattle  of  the  British  Is- 

1  Farmers'  Magazine,  1841,  vol.  XIV,  p.  50. 


IN-BREEDING  225 

lands.  These  cattle  have  been  kept  pure  in  various 
private  parks  of  Great  Britain  and  have  for  many  hundred 
years  been  subjected  to  conditions  which  compelled 
extensive  in-breeding.  These  cattle  have  not  perished, 
they  are  not  weak  in  constitution  and  are  not  decreasing 
in  size.  This  example  is  often  quoted  as  an  argument 
in  favor  of  in-breeding.  Darwin's  critical  analysis  of 
this  classic  example  leaves  us  still  in  doubt  as  to  its  value 
as  a  demonstration  of  the  beneficial  results  which  may  be 
expected  to  follow  long-continued  in-breeding. 

1  "  The  half-wild  cattle,"  says  Darwin,  "  which  have 
been  kept  in  British  parks  probably  for  400  or  500  years, 
or  even  for  a  longer  period,  have  been  advanced  by  Culley 
and  others  as  a  case  of  long-continued  inter-breeding  within 
the  limits  of  the  same  herd  without  any  consequent  injury. 
With  respect  to  the  cattle  at  Chillingham,  the  late  Lord 
Tankerville  owned  that  they  were  bad  breeders.  The 
agent,  Mr.  Hardy,  estimates  (in  a  letter  to  me  dated 
May,  1861)  that  in  the  herd  of  about  50  the  average  num- 
ber annually  slaughtered,  killed  by  fighting  and  dying, 
is  about  10,  or  one  in  five.  As  the  herd  is  kept  up  to 
nearly  the  same  average  number,  the  annual  rate  of  in- 
crease must  be  likewise  about  one  in  five.  The  bulls, 
I  may  add,  engage  in  furious  battles,  of  which  battles 
the  present  Lord  Tankerville  has  given  me  a  graphic 
description,  so  that  there  will  always  be  rigorous  selec- 
tion of  the  most  vigorous  males.  I  procured  in  1855 
from  Mr.  D.  Gardner,  agent  to  the  Duke  of  Hamilton, 
the  following  account  of  the  wild  cattle  kept  in  the  Duke's 
park  in  Lanarkshire,  which  is  about  200  acres  in  extent. 
The  number  of  cattle  varies  from  65  to  80 ;  and  the  num- 
ber annually  killed  (I  presume  by  all  causes)  is  from  8 

1  Darwin,  "Animals  and  Plants  under  Domestication,"  p.  97. 
Q 


226  THE   BREEDING   OF   ANIMALS 

to  10 ;  so  that  the  annual  rate  of  increase  can  hardly  be 
more  than  one  in  six.  Now  in  South  America,  where 
the  herds  are  half-wild,  and  therefore  offer  a  nearly  fair 
standard  of  comparison,  according  to  Azara  the  natural 
increase  of  cattle  on  an  estancia  is  from  one-third  to  one- 
fourth  of  the  total  number,  or  one  in  between  three  and 
four,  and  this  no  doubt  applies  exclusively  to  adult  ani- 
mals fit  for  consumption.  Hence  the  half-wild  British 
cattle  which  have  long  been  inter-bred  within  the  limits 
of  the  same  herd  are  relatively  far  less  fertile.  Although 
in  an  unenclosed  country  like  Paraguay  there  must  be 
some  crossing  between  the  different  herds,  yet  even  there 
the  inhabitants  believe  that  the  occasional  introduction 
of  animals  from  distant  localities  is  necessary  to  prevent 
'  degeneration  in  size  and  diminution  in  fertility/  The 
decrease  in  size  from  ancient  times  in  the  Chillingham 
and  Hamilton  cattle  must  have  been  prodigious,  for 
Professor  Rutimeyer  has  shown  that  they  are  almost 
certainly  descended  from  the  gigantic  bos  primigenius. 
No  doubt  this  decrease  in  size  may  be  largely  attributed 
to  less  favorable  conditions  of  life ;  yet  animals  roaming 
over  large  parks,  and  fed  during  severe  winters,  can  hardly 
be  considered  as  placed  under  very  unfavorable  condi- 
tions." 

210.  Deer  in  parks.  —  In  many  English  parks  fallow 
deer  have  been  kept  for  many  decades,  and  in-breeding 
must   often   result.     An   investigation   by   Darwin   dis- 
closed the  fact  that  the  managers  of  such  parks  found  it 
necessary  to  introduce  new  blood  to  improve  the  size, 
constitution,  vigor  and  prevent  the  taint  of  "  rick  back," 
which  follows  too  close  breeding. 

211.  In-breeding  among  pigs.  —  The  evil  results  from 
in-breeding  are  naturally  more  quickly  apparent  among 


IN-BREEDING  227 

animals  which  produce  large  numbers  of  young  at  a  birth 
and  have  a  comparatively  short  period  of  gestation. 
Domestic  swine  fulfill  these  conditions  admirably  and 
are  therefore  most  valuable  material  for  breeding  experi- 
ments. 

"  Mr.  J.  Wright,  well  known  as  a  breeder,  crossed 
the  same  boar  with  the  daughter,  granddaughter,  and 
great-granddaughter,  and  so  on  for  seven  generations. 
The  result  was,  that  in  many  instances  the  offspring  failed 
to  breed ;  in  others  they  produced  few  that  lived ;  and 
of  the  latter  many  were  idiotic,  without  sense,  even  to 
suck,  and  when  attempting  to  move  could  not  walk 
straight.  Now  it  deserves  especial  notice,  that  the  two 
last  sows  produced  by  this  long  course  of  inter-breeding 
were  sent  to  other  boars,  and  they  bore  several  litters 
of  healthy  pigs.  The  best  sow  in  external  appearance 
produced  during  the  whole  seven  generations  was  one 
in  the  last  stage  of  descent;  but  the  litter  consisted  of 
this  one  sow.  She  would  not  breed  to  her  sire,  yet  bred 
at  the  first  trial  to  a  stranger  in  blood.  So  that,  in  Mr. 
Wright's  case,  long-continued  and  extremely  close  inter- 
breeding did  not  affect  the  external  form  or  merit  of  the 
young;  but  with  many  of  them  the  general  constitution 
and  mental  powers,  and  especially  the  reproductive  func- 
tions, were  seriously  affected." 

Nathusius  reports  that  as  a  result  of  closely  in-breed- 
ing Yorkshire  swine  for  three  generations  the  offspring 
were  weak  in  constitution  and  their  fertility  was  impaired. 

212.  In-breeding  sheep.  —  The  American  Merino  sheep 
is  a  remarkable  example  of  what  intelligent  breeding  and 

1  Darwin,  "Animals  and  Plants  under  Domestication,"  p. 
101. 

Also  Journal  of  Royal  Agricultural  Society,  1846,  vol.  7,  p.  205. 


228  THE  BREEDING  OF  ANIMALS 

selection  can  accomplish  in  the  improvement  of  the 
domestic  animals.  The  first  importation  of  Spanish 
Merino  sheep  to  America  was  made  in  1815.  The  aver- 
age weight  of  fleece  of  these  sheep  at  that  time  was 
three  or  four  pounds  a  head.  This  average  was  in- 
creased by  American  breeders  until,  in  1880,  the  average 
fleece  from  selected  flocks  was  fifteen  pounds  a  head,  and 
single  individuals  were  produced  which  sheared  as  high 
as  thirty-five  pounds.  Plumb 1  reports  that  the  heaviest 
fleece  on  record  weighed  44  pounds  and  3  ounces  and  was 
taken  from  a  two-year-old  ram  at  the  public  shearing 
of  the  Vermont  Sheep  Shearing  Association.  But  the 
finest  specimens  of  the  American  Merino  breed  were  the 
result  of  in-breeding.  "  Mr.  Atwood  bred  his  entire  flock 
from  one  ewe,  —  and  thus,  after  being  drawn  beyond  all 
doubt  from  an  unmixed  Spanish  Cabana,  they  have 
been  bred  in-and-in,  in  the  United  States,  for  upward 
of  sixty  years."2  "The  ram  Gold  Drop  for  which  Mr. 
Hammond  refused  twenty-five  thousand  dollars,"  3  was 
closely  in-bred. 

213.  In-breeding  dogs.  —  Many  examples  of  in-breed- 
ing among  dogs  are  mentioned  in  the  literature  of  breed- 
ing, but  unfortunately  the  records  of  these  cases  are  very 
incomplete  and  many  are  of  doubtful  scientific  value. 
The  author  has  had  an  opportunity  to  examine  somewhat 
carefully  the  results  of  long-continued  in-breeding  among 
fox  terriers.  Arthur  Rhys,  the  herdsman  at  the  University 
of  Missouri,  has  practiced  very  close  in-breeding  of  fox 
terriers  for  nine  generations.  Daughter  No.  1,  from 
wholly  unrelated  parents,  was  bred  back  to  Designer,  her 

1  Plumb,  "Types  and  Breeds  of  Farm  Animals,"  p.  349. 

2  Randall,  "Practical  Shepherd." 

3  Miles,  "Stock  Breeding,"  p.  150. 


\ 


a§^* 

m:- 


-T--W.1 


4    -..*.-.- 


PLATE  XIV. —  Upper.  Close  in-breeding  of  fox  terrier.  "Dis- 
patcher" at  age  nine  months;  ninth  generation  of  intense  in-breeding. 
Lower.  "Designer  2d"  at  age  four  months;  eighth  generation  of  in- 
tense in-breeding. 


IN-BREEDING  229 

own  sire,  producing  two  litters  of  six  and  seven  each. 
Female  No.  2,  a  daughter  of  No.  1,  was  bred  to  Designer, 
her  own  sire,  who  was  also  her  grandsire.  She  produced 
a  litter  of  eight.  Female  No.  3,  a  daughter  of  No.  2, 
was  bred  again  to  Designer,  her  own  sire,  who  was  also 
her  grandsire  and  great-grandsire.  Female  No.  4  was 
again  bred  to  Designer,  her  own  sire,  who  was  also 
her  grandsire,  great-grandsire  and  great-great-grandsire. 
She  produced  a  litter  of  eight.  Thus  in  turn  Females 
Nos.  5,  6,  7  and  8  were  bred  to  their  own  sire,  Designer. 
Female  No.  8,  resulting  from  this  long-continued  in-breed- 
ing, was  bred  to  her  own  son,  and  from  the  litter  result- 
ing a  brother  arid  sister  were  selected  and  in-bred.  Mr. 
Rhys  states  that,  "  I  see  no  evidence  of  decrease  in  size 
of  bone,  in  constitution  or  in  fertility  as  a  result  of  my 
experience  in  in-breeding  fox  terriers."  The  only  pecul- 
iarity which  has  been  observed  in  the  later  generations 
as  compared  with  the  original  animals  is  a  slight  lack  of 
courage  or  "  nerve  "  in  the  later  animals.  A  normal  fox 
terrier  never  flinches  in  the  face  of  sudden  danger. 

The  illustration,  Plate  XIV,  lower,  represents  Designer 
II,  at  four  months  old,  one  of  the  seven  dogs  in  the 
eighth  generation  of  continuous  in-breeding.  Every  litter 
for  eight  generations  was  sired  by  Designer  I.  The  illus- 
tration, Plate  XIV,  upper,  pictures  the  dog  Dispatcher  of 
the  ninth  generation,  son  of  own  brother  and  sister. 

214.  Cornevin's 1  experiments.  —  The  French  breeder 
and  author,  Cornevin,  practiced  in-breeding  with  swine, 
cattle  and  sheep  for  considerable  periods  without  injury. 
He  in-bred  Jersey  cattle  for  seven  years,  Hollander  cattle 
for  twelve  years,  and  Merino  sheep  eleven  years  without 
observing  any  evidences  of  degeneracy.  His  experi- 

1  Cornevin,  "Traite  de  Zootechnie  Generate  "  (1891). 


230  THE  BREEDING   OF  ANIMALS 

ments  with  swine  were  unfavorable  to  the  practice  of 
in-breeding.  According  to  Cornevin,  among  pigeons  it 
is  the  rule  for  brother  and  sister  to  mate.  The  same 
is  also  generally  true  of  ducks,  geese,  guinea  fowls 
and  swans.  After  eleven  years  of  in-breeding  pigeons 
and  geese,  he  was  unable  to  observe  any  changes  in 
color,  weight  or  fecundity  which  could  be  ascribed  to 
in-breeding. 

Georg  Wilsdorf,1  the  German  authority,  has  found 
by  investigation  that  most  pure  breeds  have  resulted 
from  in-breeding.  He  says,  "  In  our  studies  of  the  his- 
tory of  various  breeds,  we  next  made  the  astonishing 
discovery  that  the  best  living  individuals  belonged  to 
families  which,  when  their  pedigrees  were  traced,  were 
found  all  to  come  from  a  single  family  —  often  from  a 
single  individual.  By  way  of  illustration  I  might  cite 
the  Hanoverian  halfbloods,  which  we  know  particularly 
through  the  studies  of  de  Chapeaurouge  and  Grabensee 
to  have  come  almost  altogether  from  three  stallions,  of 
which  Norfolk  has  hitherto  had  the  greatest  influence  on 
the  breed  —  an  influence  that  is  increasing  all  the  time. 
Researches  into  the  swine  breeding  of  the  Visselhovede 
district,  and  into  that  of  Hildesheim  in  Bavaria,  have 
shown  that  in  each  case  a  single  boar  was  the  ancestor 
of  various  valuable  families,  to-day  widely  scattered. 
And  Hoesch  of  Neukirchen  has  found  that  his  valuable 
strain  of  swine  is  principally  due  to  the  blood  of  a  single 
early  boar  Richard." 

"  The  modern  science  of  breeding,  however,  stands 
firm  in  its  belief  that  for  the  production  of  definite  types 
for  special  purposes  in-breeding  is  the  quickest  and  most 
certain  method  of  procedure,  and  all  great  breeders  who 

1  Journal  of  Heredity,  March,  1915,  pp.  110-111. 


IN-BREEDING  231 

work  toward  any  particular  goal  depend  largely  on  in- 
breeding, knowingly  or  unknowingly."  1 

215.  Weismann's  and  Von  Guaita's  experiments.  — 
Weismann 2  in-bred  mice  for  twenty-nine  generations.  As 
shown  in  the  following  table,  there  was  a  constant  and 
fairly  uniform  decrease  in  fertility  from  the  first  to  the 
last  generation : 

1  to  10  generations ;  1345  young ;  219  litters ;  avg.  per  litter 

6.1 

11  to  20  generations;  252  young;  62  litters;  avg.  per  litter 

5.6 

21  to  29  generations;  124  young;  29  litters;  avg.  per  litter 

4.2 

The  average  number  of  young  to  a  litter  decreased  from 
6.1  in  the  first  ten  generations  to  4.2  in  the  last  ten  genera- 
tions. Whether  this  decrease  is  due  directly  to  the  specific 
action  of  in-breeding  on  the  quality  of  fertility,  or  whether 
it  simply  represents  an  intensification  of  an  innate  tend- 
ency to  low  fertility  which  existed  in  this  particular  strain, 
it  is  not  possible  to  determine.  Von  Guaita,  working 
with  the  same  strain  of  mice  and  beginning  with  the 
last  generation  (29th)  bred  by  Weismann,  obtained  the 
following  results: 

1st  and  2d  generations,  avg.  per  litter,  3.5 
3d  and  4th  generations,  avg.  per  litter,  3.6 
5th  and  6th  generations,  avg.  per  litter,  2.9 

There  is  here  a  clear  loss  of  fertility  from  an  average 
of  6.1  to  a  litter  to  2.9  to  a  litter  in  35  generations,  trace- 
able to  in-breeding. 

1  Georg  Wilsdorf,  "Tierzuchtung,"  1912. 

2  "Berichte  der  Naturforschenden  Gesellschaft  zu  Freiburg," 
1900. 

See  Morgan,  "Experimental  Zoology,"  p.  188. 


232  THE  BREEDING  OF  ANIMALS 

216.  Researches  of  Ritzema  Bos.  —  An  interesting 
experiment  with  in-breeding  white  rats  for  thirty  genera- 
tions is  reported  by  Ritzema  Bos.1  Beginning  with  an 
albino  female  mated  with  a  wild  rat,  the  first  mating  re- 
sulted in  twelve  offspring.  Seven  of  this  litter  were 
bred  .to  a  white  male  but  unrelated.  The  resulting  off- 
spring were  closely  in-bred  for  six  years.  The  matings 
were  brothers  to  sisters  and  parents  to  offspring.  The 
average  size  of  the  litters  for  twenty  generations  and 
covering  a  period  of  four  years  remained  practically 
constant.  The  last  ten  generations  born  during  the 
last  two  years  of  the  experiment  showed  a  decided  decrease 
in  the  fertility  of  the  matings.  The  average  size  of 
litters  by  years  is  shown  in  the  table. 

DECREASED  FERTILITY  DUE  TO  IN-BREEDING.     (Bos) 

1887      1888      1889      1890      1891      1892 

71  71  7H  6H  4&  3t 

Not  only  the  average  size  of  the  litters  decreased  in 
thirty  generations  from  7J  to  3 J,  but  the  number  of  mat- 
ings which  were  sterile  increased  greatly  from  the  first 
to  the  last  generations,  as  shown  in  the  following  table : 

MATINGS  WHICH  PROVED  STERILE.     (Bos) 

1887      1888      1889      1890      1891      1892 

0  2.63          5.55         17.39          50  41.18 

There  is  evidence  also  in  this  experiment  that  the 
constitutional  vigor  of  the  offspring  of  parents  which 
were  the  result  of  long-continued  in-breeding  was  materi- 
ally injured.  The  time  of  the  appearance  of  weakness 

1  Ritzema  Bos,  "Biol.  Centralb.,"  XIV,  1894.  See  also  Mor- 
gan, "Experimental  Zoology,"  p.  188. 


IN-BREEDING  233 

in  the  offspring  was  coextensive  with  the  decline  in 
fertility. 

The  comparative  mortality  of  the  young  increased 
rapidly,  as  shown  in  the  following  table : 

INCREASED  RATE  OF  MORTALITY  DUE  TO  IN-BREEDING.    (Bos) 

1887  1888  1889  1890  1891  1892 

Per  cent       Per  cent        Per  cent       Per  cent        Per  cent       Per  cent 

3.9  4.4  5.0  36.7  36.4          45.5 

The  bad  effects  from  in-breeding  were  more  noticeable 
when  brother  and  sister  were  mated  than  when  parents 
were  mated  with  offspring.  Of  the  matings  between 
parent  and  offspring  21.4  per  cent  were  sterile,  while 
those  between  brother  and  sister  were  36  per  cent  infertile. 
A  tendency  to  decrease  in  size  is  indicated  by  the  record 
of  weights  of  different  generations.  Full-grown  male 
rats  of  the  first  generation  weighed  300  grams  each.  In 
the  tenth  generation  the  weight  had  decreased  to  275 
grains  and  at  the  end  of  six  years  the  weight  of  rats  had 
declined  to  240  grams. 

217.  The  Wistar  Institute  experiments.  —  Extensive 
in-breeding  experiments  by  Helen  Dean  King l  at  the 
Wistar  Institute,  Philadelphia,  with  white  rats  seem  to 
have  resulted  in  disproving  the  theory  that  in-breeding 
is  always  and  necessarily  followed  by  evil  results.  In 
this  investigation  white  rats  have  been  as  closely  in-bred 
as  possible  for  twenty-two  generations.  More  than 
10,000  in-bred  rats  have  been  observed  during  a  period 
of  seven  years.  The  original  stock  was  two  pairs  of 
albino  rats.  Each  pair  was  used  as  the  foundation  for  a 
series  of  in-breeding  experiments.  In  each  generation 

1  Journal  of  Heredity,  vol.  7  (1916),  p.  70. 


234  THE   BREEDING  OF  ANIMALS 

the  best  rats  from  the  standpoint  of  size,  vigor,  fecundity 
and  general  quality  were  carefully  selected. 

The  actual  results  of  this  investigation  after  twenty- 
two  generations  of  in-breeding  are  that  the  male  in-bred 
rats  are  about  fifteen  per  cent  heavier  and  the  female 
in-bred  rats  about  three  per  cent  heavier  than  stock  rats. 
The  size  of  litters  among  the  stock  rats  has  been  seven, 
while  among  the  in-bred  rats  the  litters  have  increased 
and  now  average  seven  and  four-tenths  each.  The  thrift 
and  vigor  of  in-bred  rats  in  these  experiments  was  appar- 
ently not  injured  by  in-breeding.  "  The  results  so  far 
obtained  with  these  rats,"  says  Dr.  King,  "  indicate 
that  close  in-breeding  does  not  necessarily  lead  to  a  loss 
of  size  or  of  constitutional  vigor  or  of  fertility,  if  the 
animals  so  mated  come  from  sound  stock  in  the  beginning 
and  sufficient  care  is  taken  to  breed  only  from  the  best 
individuals." 

218.  In-breeding  Berkshires  by  Mr.  Gentry.  —  The 
remarkable  success  which  may  follow  the  practice  of 
in-breeding  when  intelligently  conducted  by  a  skillful 
breeder  is  shown  in  the  experience  of  N.  H.  Gentry  of 
Sedalia,  Missouri.  Probably  no  American  breeder  has 
been  so  successful  in  developing  all  those  desirable  qualities 
in  Berkshire  swine  which  give  this  breed  its  great  economic 
value.  At  the  Chicago  World's  Fair  in  1893  Gentry's 
Berkshires  won  twenty-three  of  the  twenty-eight  first 
prizes  offered,  and  many  of  the  other  winners  were  de- 
scended from  stock  bred  by  him.  At  the  St.  Louis  World's 
Fair  in  1903,  all  the  Berkshires  which  came  within  the 
five  cash  prizes  offered,  with  three  exceptions,  were  de- 
scended from  animals  bred  by  Gentry.  The  entire 
Gentry  herd  was  strongly  in-bred,  carrying  a  very  high 
proportion  of  the  blood  of  Longfellow.  Describing  his 


IN-BREEDING  235 

breeding  practice,  Gentry  says:1  "It  has  long  been  con- 
ceded that  Longfellow  16,835  was  the  greatest  boar  known 
to  the  breed,  in  this  country  at  least.  He  was  out  of  an 
imported  sow  and  one  of  the  best  I  ever  saw.  His  sire, 
Charmar's  Duke  13,360,  I  bred,  and  he  was  a  great  one, 
too.  He  was  sired  by  an  imported  boar  and  was  out  of 
an  imported  sow,  and  this  sow  and  the  dam  of  Longfellow 
were  got  by  the  same  boar.  After  the  death  of  Charmar's 
Duke  13,360,  which  happened  when  he  was  only  a  two- 
year-old,  I  kept  his  best  son,  Longfellow,  and  after  Long- 
fellow's death  his  best  sons,  and  after  their  death,  their 
best  sons.  Thus  Longfellow,  Longfellow's  sons,  and  now 
his  grandsons,  have  followed  each  other  in  use  on  my  herd. 
One  of -the  largest  and  best  boars  I  have  ever  produced, 
one  which  I  showed  at  the  World's  Fair  at  Chicago  in 
1893,  weighing  at  13  months  and  6  days  of  age,  660  pounds, 
with  as  much  action,  strength,  vigor  and  masculine 
development  as  any  boar  I  ever  saw,  was  produced  by  a 
son  of  Longfellow  out  of  a  daughter  of  Longfellow  sired 
by  the  sire  of  Longfellow.  Thus  the  three  top  successive 
sires  in  his  pedigree  were  the  sire  of  Longfellow,  Longfellow 
and  a  son  of  Longfellow.  I  could  name  many  good  ones 
bred  as  closely  and,  in  fact,  almost  every  animal  in  my 
herd  has  been  produced  by  as  close  in-breeding  on  both 
sides."  (See  Plate  XV.) 

"  I  have  practiced  in-breeding  more  from  necessity 
than  from  any  other  reason.  I  believe  I  have  not  used  a 
boar  other  than  my  own  breeding  for  twenty  years." 

After  a  lifetime's  experience  with  in-breeding  the 
conclusions  of  Gentry  are  significant :  "  If  it  is  true  that 
in-breeding  intensifies  weakness  of  constitution,  lack  of 
vigor,  or  too  great  fineness  of  bone,  as  we  all  believe,  is 

1  Gentry,  Amer.  Breeders'  Assoc.,  vol.  I,  1905,  pp.  170-171. 


236  THE  BREEDING  OF  ANIMALS 

it  not  as  reasonable  and  as  certain  that  you  can  intensify 
strength  of  constitution,  heavy  bone,  or  vigor,  if  you  have 
those  traits  well  developed  in  the  blood  of  the  animals 
you  are  in-breeding  ?  I  think  I  have  continued  to  improve 
my  herd,  being  now  able  to  produce  a  larger  percentage 
of  really  superior  animals  than  at  any  time  in  the  past ..." 

Another  noted  breeder  of  Berkshires  who  attributes 
the  high  quality  of  his  animals  to  the  practice  of  in-breed- 
ing is  A.  J.  Lovejoy  of  Illinois.  'He  is  quoted  in  Daven- 
port's "  Principles  of  Breeding  "  as  follows : 

1  "  We  are  believers  in  quite  close,  even  in-breeding. 
We  find  the  greatest  show  animals  are  closely  in-bred. 
Sires  to  half-sisters  is  the  most  common  form  of  close 
breeding,  though  cousins,  nephews,  and  nieces,  and  even 
brothers  and  sisters  are  bred  together  with  great  success. 
It  of  course  requires  good  judgment  in  mating  animals 
that  are  particularly  strong  in  individual  merit.  Should 
each  have  a  bad  defect  in  any  way,  we  should  expect 
that  to  be  more  manifest  in  the  offspring  than  in  the  par- 
ents, and  likewise  the  good  points  would  be  better;  so 
if  one  mates  equally  good  specimens  the  produce  will  be 
an  improvement.  There  is  no  sire  of  any  breed  so  pre- 
potent as  an  in-bred  sire.  When  we  get  to  the  point 
where  we  feel  the  need  of  outside  blood  we  mate  an  im- 
ported sow  with  our  best  boar,  and  from  this  litter  we 
select  a  boar  to  use  on  the  get  of  his  own  sire  from  other 
sows  in  the  herd ;  that  is,  we  breed  this  boar  on  his  own 
half-sisters." 

219.  In-breeding  corn.  —  Many  of  the  principles  which 
are  now  universally  accepted  as  guides  to  practice  in 
animal-breeding  were  first  discovered  by  plant-breeders. 
The  mendelian  principle  is  a  good  example  of  this  fact. 

1  Davenport,  "Principles  of  Breeding,"  p.  625. 


IN-BREEDING  237 

While  the  fundamental  principles  governing  the  trans- 
mission of  characters  are  the  same  in  plants  and  animals, 
the  practical  applications  are  sometimes  widely  different. 
Wholesale  advice  based  wholly  upon  plant  investigations, 
therefore,  and  intended  to  guide  the  practical  breeder 
of  animals  is  not  always  justified  for  obvious  reasons. 
The  experiments  conducted  for  the  purpose  of  testing 
the  effects  of  in-breeding  on  Indian  corn  (Zea  Mays)  have 
been  extensive.  In  every  case,  so  far  as  the  author  has 
been  able  to  determine,  in-breeding  corn  has  resulted  in 
decreased  yields  if  long  continued.  Hayes1  and  East 
found  that  "  the  first  generation  of  in-breeding  has  the 
greatest  detrimental  effect."  The  injury  from  in-breed- 
ing is  not  continuous,  but  results  in  separating  the  pure 
lines  in  a  variety.  When  once  a  pure  line  is  produced 
by  in-breeding,  further  in-breeding  apparently  does  not 
reduce  the  yield.  Shamel  2  found  that  four  generations 
of  self-fertilization  of  corn  so  weakened  the  strain  that 
the  seed  failed  to  germinate.  Darwin,  experimenting 
with  morning  glories  (Ipomsea)  for  a  period  of  ten  years, 
found  that  the  strain  which  was  screened  so  that  insects 
could  not  bring  about  cross-fertilization  lost  in  vigor 
as  compared  with  a  similar  strain  which  had  beeen  left 
in  the  open  and  cross-fertilized  through  the  agency  of 
insects. 

Wheat  is  a  self-fertilizing  plant.  Unnumbered  genera- 
tions of  in-breeding  seem  not  to  have  decreased  its  vigor 
or  lowered  its  fertility.  Castle  in-bred  brother  and  sister 
of  Drosophila  (pomace  fly)  for  59  generations.  No  loss 
of  fertility  or  vigor  was  observed. 

1  Hayes  and  East,  Bui.  168,  Connecticut  Agricultural  Experi- 
ment Station,  p.  11. 

2  Shamel,  U.  S.  Dept.  of  Agr.,  Year  Book,  1905,  p.  388. 


238  THE   BREEDING  OF  ANIMALS 

Among  the  domestic  animals  it  is  quite  probable  that 
the  effects  of  in-breeding  on  different  species  will  differ 
materially. 

220.  How  long  is  it  safe  to  continue  in-breeding.  — 
If  we  limit  the  application  of  the  term  in-breeding  to  mat- 
ings  between  parent  and  offspring  or  between  brother 
and  sister,  then  we  cannot  escape  the  conclusion  that 
long-continued  in-breeding  results  in  decreasing  fertility, 
and  probably  also  weakens  the  constitution  and  decreases 
the  size  of   the    offspring.     * "  Continued    in-breeding," 
says  Kraemer,   "  always  must  result  in  weakened  con- 
stitution through  its  own  influence."     But  such  results 
follow  long-continued  in-breeding.     What  are  the  limits 
of  safety?     How  long  may  the    domestic    animals    be 
closely  in-bred   without   injury?    An    answer    to  these 
questions  is  only  possible  when  all  the  conditions  are 
known,  including  a  knowledge  of  the  inherited  tendencies 
of  the  in-bred  animals.     But  it  seems  entirely  safe  to 
conclude  from  the   evidence  available  that  the  almost 
universal  prejudice  against    the  practice  of  in-breeding 
is  in  a   large    degree    unwarranted.     Such    a   prejudice 
has  undoubtedly  limited  the  usefulness  of  many  valuable 
breeding  animals  and  has  caused  real  economic  loss  to 
many  breeders. 

221.  Selection  important.  —  The  practice  of  in-breed- 
ing will  never  be  successful  in  the  absence  of  rigorous 
selection.     As  the  undesirable  qualities  are  transmitted 
with  the  same  intensity  as  the  good,  constant  vigilance 
is  required  to  guard  against  bringing  forward  latent  char- 
acters  which   are   less   desirable.     Particularly   animals 

1  Kraemer,  "Mitteilung  der  Deutsches  Landwirtschafts 
Gesellschaft,"  September,  1913.  See  also  Journal  of  Heredity, 
1914,  p.  226. 


IN-BREEDING  239 

which  are  undersize,  weak  in  constitution,  or  that  show  a 
tendency  to  low  fertility  should  not  be  in-bred.  It  is 
not  always  possible  to  detect  the  presence  of  these  tend- 
encies in  a  single  generation,  hence  a  knowledge  of  family 
history  and  pedigree  is  important.  Given  an  animal 
of  unusual  merit  with  strong  constitution,  good  size  and 
strongly  fertile,  the  breeder  runs  little  risk  in  practicing 
in-breeding  for  a  limited  time. 

222.  The  truth  about  in-breeding.  —  In  the  midst  of 
such  diversity  of  opinion  as  exists  concerning  the  results 
and  value  of  in-breeding,  the  practical  breeder  may  well 
be  puzzled.  Sweeping  generalizations  either  for  or  against 
the  practice  are  apparently  unwise  at  this  time.  An 
unreasoning  prejudice  against  the  practice  will  result  in 
withholding  from  breeders  a  valuable  method  of  breed- 
ing which  has  been  in  many  cases  the  chief  reliance  of 
the  world's  greatest  improvers  of  the  domestic  animals. 
On  the  other  hand,  a  blind  following  of  those  enthusiasts 
who  have  claimed  for  in-breeding  some  mysterious  power 
in  the  improvement  of  animal  character  will  certainly 
lead  to  disaster. 

The  practice  of  in-breeding  has  been  compared  to  a 
powerful  medicine  which  in  the  hands  of  a  skillful  physi- 
cian may  decide  the  issues  of  life,  but  in  the  hands  of  the 
novice  becomes  a  dangerous  and  often  fatal  instrument. 
In-breeding  may  be  practiced  successfully,  but  only  by 
those  who  are  familiar  with  the  biological  principles 
involved,  and  who  are  familiar  with  the  results  which 
sometimes  follow  the  mating  of  nearly  related  animals  and, 
what  is  quite  as  important,  who  know  the  ancestral  his- 
tory of  their  breeding  stock. 

Whether  we  accept  the  view  that  evil  is  an  incidental 
result  due  to  the  intensification  of  undesirable  qualities 


240  THE  BREEDING  OF  ANIMALS 

already  existing  in  the  germ-plasm  of  the  parent  stock,  or 
whether  we  hold  that  certain  definite  evils  are  a  necessary 
result  of  mating  animals  of  near  kin,  we  must  admit  that 
in-breeding  has  often  been  practiced  with  great  success 
and  no  appreciable  injury.  It  is,  therefore,  clearly  appar- 
ent that  there  are  conditions  which  are  neither  unusual 
nor  extremely  rare  under  which  in-breeding  can  be  prac- 
ticed with  the  assurance  of  success. 

223.  Fixing  characters  by  in-breeding.  —  In-breeding 
has  been  a  powerful  means  of  fixing  and  perpetuating 
valuable  characteristics  in  the  domestic  animals.  It  is 
still  a  valuable  method  to  be  employed  for  the  same  pur- 
pose. But  in-breeding  is  only  a  means  to  an  end  and  not 
the  end.  In-breeding  possesses  no  magic  or  occult  power 
which  will  be  exerted  for  the  improvement  of  animals. 
While  it  works  powerfully  in  fixing  the  good  qualities, 
it  is  no  less  potent  in  firmly  establishing  undesirable 
qualities  which  may  be  present  in  the  parent  stock.  And 
in  this  fact  lies  the  chief  danger  from  in-breeding.  In 
fixing  the  good  characters,  we  may  unconsciously 
strengthen  the  powers  of  transmission  in  the  direction 
of  bad  qualities.  The  most  skillful  breeders  are  less 
likely  to  err  in  the  direction  of  perpetuating  tendencies 
to  evil,  and  history  gives  ample  confirmation  of  the  cer- 
tain good  which  does  follow  in-breeding  when  practiced 
with  intelligence  by  skillful  and  experienced  breeders 
and  accompanied  by  rigorous  selection. 

It  has  often  happened  in  the  experience  of  breeders  that 
a  sudden  mutation  has  appeared  in  a  single  animal.  This 
mutation  may  represent  a  high  degree  of  improvement  in  a 
certain  character  or  characters  which  the  breeder  has 
long  sought  to  develop  in  his  breeding  stock.  This 
variation  appears  in  one  animal  only.  It  is  highly 


IN-BREEDING  241 

desirable  not  only  to  perpetuate  this  improved  character 
but  to  breed  animals  that  have  this  quality  in  as  pure 
and  dominant  a  state  as  in  the  original  animal.  This 
can  be  accomplished  by  in-breeding.  No  other  method 
is  available  which  will  so  quickly  and  certainly  result  in 
producing  offspring  of  similar  or  identical  blood  lines. 
The  history  of  animal-breeding  is  rich  in  instances  of 
great  animals,  famous  for  their  individual  excellence 
but  more  famous  because  they  have  left  a  heritage 
of  potent  "  blood  "  which  has  established  a  new  and 
better  strain  or  even  a  new  breed.  We  need  only 
recall  the  names  of  Favourite,  the  Shorthorn  bull,  Justin 
Morgan,  the  founder  of  the  Morgan  breed,  Hambletonian 
10,  the  forerunner  of  the  American  trotting  horse,  and 
scores  of  individuals  of  lesser  note  belonging  to  practically 
every  modern  breed.  In  many  of  the  instances  to  which 
reference  is  here  made,  the  great  individuals  would  never 
have  become  famous  if  breeders  had  not  recognized  their 
peculiar  excellences  and  have  insured  the  perpetuation 
of  their  valuable  characters  by  in-breeding. 

224.  In-breeding  and  prepotency.  —  The  prepotency 
of  animals  is  increased  by  in-breeding.  There  is  unanimity 
among  investigators  and  practical  breeders  on  this  point. 
By  continuous  in-breeding  we  may  "  breed  out  "  less 
desirable  qualities,  that  is,  in  the  light  of  mendelism  the 
characters  in  the  germ-plasm  tend  to  become  homozygous. 
In-bred  animals  are  "  pure-bred  "  animals  not  only  in  the 
parlance  of  the  breeder  but  also  from  the  standpoint  of 
genetics.  Mating  animals  of  diverse  characters  tends 
to  destroy  prepotency.  Mixing  the  blood  of  animals  of 
widely  differing  characteristics  results  in  making  the 
constituent  characters  of  the  germ-plasm  heterozygous. 
The  cross-bred  animal  is  never  prepotent. 


242  THE   BREEDING   OF  ANIMALS 

225.  Results  of  in-breeding  vary  with  different  species. 
—  The  varying  opinions  regarding  the  benefits  or  injuries 
from  in-breeding  may  in  part  be  accounted  for  from  the 
fact  that  investigators  have  based  their  conclusions  upon 
data  gathered  from  researches  on  widely  differing  species 
of  animals  and  plants.  The  effects  of  in-breeding  are  quite 
different  in  different  species  or  families.  Among  plants, 
nature  seems  to  have  designed  some  species  especially  to 
insure  cross-fertilization  and  to  guard  against  self-fertili- 
zation, while  other  species  are  self-fertilizing.  Indian 
corn  (Zea  Mays)  is  a  good  example  of  the  former  class 
of  plants.  The  results  of  continuous  in-breeding  on  the 
maize  plant  are  markedly  injurious.  Shull  found  that 
continual  self-fertilization  in  Indian  corn  resulted  in  a 
loss  of  vigor.  There  are  other  plants  like  wheat  that  are 
self -fertilizing,  and  it  is  difficult  to  see  how  in-breeding 
can  be  injurious  in  such  species. 


CHAPTER  XII 
CROSS-BREEDING 

THE  term  crossing  or  cross-breeding,  like  the  term 
in -breeding,  is  not  capable  at  this  time  of  exact  definition. 
In  general  we  may  define  cross-breeding  as  the  mating  of 
individuals  which  are  not  related.  The  literature  of  the 
subject  indicates  that  this  term  has  been  loosely  applied. 
Some  indeed  have  used  the  term  to  designate  the  mating 
of  individuals  belonging  to  different  families  within  the 
same  breed.  As  a  rule,  cross-breeding  means  the  mating 
of  individuals  belonging  to  different  breeds,  as  a  cross 
between  the  Shorthorn  and  Hereford;  or  the  union  of 
animals  belonging  to  different  species,  as  a  cross  between 
the  stallion  and  the  jennet.  Cross-breeding  has  been 
strongly  recommended  by  some  breeders  as  a  valuable 
method  of  improving  the  domestic  animals. 

226.  Permanent  and  temporary  results  of  cross-breed- 
ing. —  In  recommending  cross-breeding,  the  advocates  of 
this  practice  have  not  always  been  careful  clearly  to 
differentiate  between  the  permanent  and  lasting  results 
of  cross-breeding  and  the  more  immediate  and  tem- 
porary advantages.  The  effect  of  cross-breeding  upon 
the  purity  of  the  heritable  characters  of  the  breed  as 
represented  by  the  germinal  elements  in  the  germ-plasm 
is  one  thing,  while  the  more  or  less  temporary  effect  on  the 
body-cells  may  be  quite  another  thing.  The  purpose  of 
the  breeder  of  pure-bred  registered  animals  is  to  establish 

243 


244  THE   BREEDING   OF   ANIMALS 

a  race  of  animals  that  will  breed  true.  It  matters  not  how 
many  good  qualities  the  individual  breeding  animal  may 
possess;  if  he  cannot  transmit  these  good  qualities  to 
his  offspring,  he  is  not  a  desirable  animal  for  breeding 
purposes.  He  may  be  valuable  for  commercial  purposes. 
Such  an  animal  might  be  a  fast  horse,  a  prize-winning 
beef  animal,  or  a  great  producing  cow,  but  lacking  the 
ability  to  transmit  these  qualities  this  animal  would  not 
be  a  desirable  or  valuable  individual  in  a  breeding  herd. 
It  may  be  quite  possible,  therefore,  for  a  method  of  breed- 
ing to  have  a  distinct  economic  value  for  the  production 
of  commercial  animals  and  at  the  same  time  be  a  very 
bad  method  for  the  breeder  of  improved  live-stock  whose 
purpose  is  to  produce  animals  for  breeding  purposes  and 
not  for  slaughter  or  work.  What  effect  does  cross-breed- 
ing have  on  the  breeding  powers  of  the  domestic  animals  ? 
What  value,  if  any,  has  cross-breeding  in  the  production 
of  animals  for  commercial  purposes  and  which  are  not 
intended  to  be  used  for  breeding  ?  The  breeder's  interest 
in  cross-breeding  will  naturally  center  about  the  relations 
of  this  practice  to  heredity. 

227.  Advantages  from  cross-breeding.  —  Breeders  of 
the  domestic  animals  have  frequently  practiced  cross- 
breeding in  the  belief  that  certain  very  definite  and  specific 
benefits  followed  such  practice.     In  attempting  to  analyze 
the  reasons  for  practicing  cross-breeding,  it  is  apparent 
that  this  has  been  generally  followed  for  one  or  more  of 
the  following  reasons,  —  to  increase  fertility,  to  restore 
weakened  constitution,  to  increase  the  size  or  for  improve- 
ment. 

228.  Grading.  —  The  practice  of  grading,  by  which 
is  meant  the  improvement  of  native  or  unimproved  ani- 
mals by  mating  with  pure-bred  or  registered  animals, 


CROSS-BREEDING  245 

should  not  be  confused  with  cross-breeding.  Cross- 
breeding is  the  union  of  two  or  more  distinct  races  or 
breeds,  while  grading  is  an  attempt  gradually  to  develop 
a  type  by  continually  breeding  to  pure-bred  sires. 

Grading  is  one  of  the  most  successful  and  certain 
methods  of  improvement.  There  are  many  examples 
of  successful  grading  among  the  breeders  of  domestic  ani- 
mals. Manifestly  the  more  inferior  the  foundation  mother 
stock,  the  greater  will  be  the  improvement  when  mated  to 
a  pure-bred  registered  sire.  A  few  generations  will  often 
suffice  to  produce  "  high-grade  "  cattle,  horses,  sheep  or 
swine  that  will  possess  most  of  the  valuable  qualities 
which  have  commercial  value.  For  commercial  or  eco- 
nomic purposes,  the  high-grade  beef  animal  may  be  as 
valuable  as  the  pure-bred.  A  high-grade  dairy  cow  will 
often  produce  as  much  milk  and  butter  as  the  registered 
cow.  For  breeding  purposes,  the  pure-bred  registered 
animal  is  far  superior.  The  grade  does  not  transmit  its 
qualities  with  certainty.  One  object  of  pure  breeding 
is  to  develop  the  quality  of  prepotency,  and  this  is  accom- 
plished by  long  years  of  most  careful  selection  and  mat- 
ing. The  grade  animal  cannot  possibly  possess  the 
quality  of  prepotency  to  the  same  extent  as  the  pure- 
bred form,  hence  it  follows  that  even  if  the  grade  does 
exhibit  a  high  degree  of  individual  merit,  this  is  no  evi- 
dence of  ability  to  transmit  the  same  qualities  to  the 
offspring.  A  high  degree  of  individual  excellence  in  a 
pure-bred  registered  animal  is  more  certain  to  be  trans- 
mitted, and  for  this  reason  the  registered  animal  of  high 
merit  is  often  held  by  the  experienced  breeder  at  values 
which  seem  beyond  any  real  economic  basis. 

229.  Cross-breeding  to  increase  fertility.  —  Some  ani- 
mals are  infertile  when  bred  to  other  individuals  of  their 


246  THE  BREEDING  OF  ANIMALS 

own  breed.  This  is  particularly  the  case  if  the  two  ani- 
mals mated  are  the  result  of  long-continued  in-breeding 
and  are  themselves  also  near  of  kin. 

In  the  instance  of  in-breeding  pigs  by  J.  Wright  already 
cited,  the  seventh  generation  resulting  from  close  in- 
breeding consisted  of  one  sow.  This  sow  was  infertile 
when  bred  to  her  sire,  but  bred  readily  with  an  unrelated 
boar.  Darwin  cites  numerous  instances  of  increased 
fertility  due  to  crossing.  Mr.  Eyton,1  a  breeder  of  Grey 
Dorkings,  found  it  necessary  to  increase  the  prolificacy 
and  increase  the  size  of  his  in-bred  stock  by  cross- 
ing. Bates,2  the  great  breeder  of  Shorthorn  cattle,  bred 
closely  in-and-in  for  thirteen  years,  but  then  found 
it  necessary  to  "  infuse  fresh  blood,  not  to  improve 
the  form  of  the  animals  but  on  account  of  lessened 
fecundity." 

Bloodhounds 3  closely  in-bred  lost  their  fertility,  which 
was  restored  by  a  single  cross. 

Many  plants  are  infertile  unless  cross-fertilized  with 
the  pollen  of  another  variety. 

230.  Cross-breeding  to  increase  size  and  restore 
constitution.  —  The  tendency  of  in-breeding  to  decrease 
the  size  is  promptly  corrected  by  cross-breeding.  "  The 
good  effects  of  a  cross  are  at  once  shown  by  the  greater 
size  of  the  offspring." 

It  is  the  common  experience  of  breeders  that  highly 
improved  strains  of  cattle,  hogs  or  sheep  sometimes  show 
a  refinement  or  delicacy  of  constitution  which  in  a  measure 
interferes  with  the  economic  value.  In  such  cases  a  sud- 
den out-cross  to  another  equally  valuable  strain  may 

1  Darwin,  "Animals  and  Plants  under  Domestication,"  vol. 
II,  p.  105. 

2  Ibid. 

3  Loc.  cit. 


CROSS-BREEDING  247 

quickly  correct  any  tendency  to  inferior  size  or  weakened 
constitution.  Not  only  are  in-bred  animals  benefited 
in  certain  definite  qualities  by  crossing,  but  breeds  and 
families  which  have  not  suffered  in  any  way  from  in-breed- 
ing are  sometimes  improved  in  size,  vigor  and  fertility 
by  crossing. 

231.  Crossing   and   heredity.  —  As  in-breeding  tends 
to  simplify  the  germ-plasm  and  strengthen  the  powers  of 
transmission,    so    cross-breeding    tends    to   weaken   the 
prepotency  and   complicate  the   elemental   constitution 
of  the  hereditary  substance.     Crossing  has  a  tendency 
to  break  up  established  characters.     It  destroys  com- 
binations of  characters  which  have  long  existed  in  the 
strain  and  which  under  systems  of  pure  breeding  have 
behaved   in   a   manner   like   unit   characters   in   trans- 
mission.    The  result   of   crossing  pure-bred   animals  is 
often  to  destroy  the  results  of  generations   of   careful 
breeding  and  selection. 

232.  First   cross  an   improvement.  —  The    cross-bred 
offspring  of  pure-bred  parents  often  show  an  improvement 
over  either  of  the  parents.     This   superiority  may  be 
exhibited  not  alone  in  increased  fertility  and  more  vigorous 
constitution,  but  also  in  the  very  qualities  which  char- 
acterize the  parents.     A  cross  between  animals  belong- 
ing to  distinct  breeds  may  be  a  better  beef  animal  than 
either  parent.     The  Scotch  farmer  breeds  the  Aberdeen 
Angus  cow  to  a  white  Shorthorn  bull.     The  offspring  is 
the  well  known  "  blue  gray  "  which  is  highly  prized  by 
the  feeder  and  in  the  fat  cattle  market  commands  a 
premium  over  the  pure-bred  animals  of  either  breed. 
The  fat  cattle  exhibitions  of  the  world  have  not  infre- 
quently given  the  highest  prizes  of  the  show  to  cross- 
bred animals.     (See  Plate  XVI.)  - 


248  THE  BREEDING  OF  ANIMALS 

But  when  it  is  attempted  to  perpetuate  the  superior 
qualities  of  the  cross-bred  animal  by  breeding,  disappoint- 
ment invariably  results.  The  second  cross  resulting 
from  the  mating  of  two  cross-bred  animals  may  be  totally 
unlike  either  of  the  immediate  parents  or  of  the  original 
pure-bred  forms.  Crossing,  therefore,  is  not  a  method  to 
be  employed  for  rapid  improvement  or  for  fixing  desir- 
able qualities.  It  is  opposed  to  in-breeding  which  does 
increase  prepotency  and  is  the  most  rapid  method  known 
of  fixing  desirable  characters. 

233.  Cross-breeding  as  a  cause  of  variation.  —  The 
fact  that  crossing  disturbs  the  balance  of  characters  and 
brings  about  recombinations  in  the  germ-plasm  gives  it  a 
peculiar  value  in  causing  variations  to  appear.  The 
breeder  who  is  working  with  pure-bred  animals  which  owe 
their  purity  of  breeding  to  a  long  period  of  careful  selec- 
tion by  skillful  breeders  cannot  hope  to  cause  any  great 
degree  of  improvement.  Pure-bred  animals  are  already 
improved.  About  all  any  breeder  working  with  pure- 
bred animals  can  do  is  to  select  out  the  highly  desirable 
strains  from  those  of  lesser  value  already  in  the  breed. 
But  as  Johanssen  has  shown,  there  are  very  definite  limits 
beyond  which  the  improvement  of  pure  lines  cannot  go. 
Marked  improvement  must  come  through  variation. 
Crossing  is  a  common  cause  of  variation.  Variations 
which  appear  as  the  result  of  crossing  may  be  desirable 
or  •  undesirable.  They  may  be  relatively  unimportant 
or  they  may  be  in  the  nature  of  a  valuable  mutation. 
Such  valuable  mutations  may  be  perpetuated  by  in -breed- 
ing and  a  new  and  valuable  quality  sometimes  secured 
in  this  way.  This  method  is  not  practical  for  breeders 
of  registered  live-stock  under  present  conditions,  but  has 
been  of  great  service  to  the  breeders  of  plants. 


PLATE  XVII.  —  Upper.  —  Half-blood  buffalo  (bison)  heifer.  The 
hybrids  are  larger  than  either  parent.  Lower.  The  bull  on  the  left  is 
five-eighths  buffalo  (bison)  and  three-eighths  Hereford.  The  animal  on 
the  right  is  a  three-quarter  blood  buffalo.  These  hybrids  are  frequently 
sterile. 


CROSS-BREEDING  249 

234.  Crossing  species.  —  Many  species  may  be  suc- 
cessfully crossed.     Some  of  these  crosses  are  of  great 
economic  value,  as  the  cross  between  the  mare  and  the  jack. 
The  number  of  successful  crosses  between  animal  species 
is  not  large.     Such  unions  are  difficult  to  make  and 
generally  sterile.     When  such  crosses  are  possible  and 
the  union  is  fertile,  the  offspring  is  generally  partially 
or  wholly  sterile.     Some  of  the  successful  crosses  which 
have  been  reported  are  the  sheep  and  goat,  horse  and  ass, 
horse  and  zebra,  cattle  and  yak,  cattle  and  bison,  brahmin 
and  domestic  cow,  game  cock  and  guinea  fowl,  domestic 
fowl  and  pheasant,  dog  and  wolf,  and  dog  and  fox. 

235.  Crossing  bison  and  cattle.  —  A  most  interesting 
experiment   in   cross-breeding    between   the    bison   and 
domestic  cattle  is  reported  by  Mossom  M.  Boyd.1    The 
hybrid  offspring  from  Hereford  dams  and  bison  sire  were 
very  uniform,  all  having  white  faces,  were  larger  than 
the  bison  and  much  smoother,  broader  and  deeper  than 
the   sire.     Great  difficulty  was  experienced   in  making 
the  first  cross  from  the  excessive  secretion  of  the  amniotic 
fluid.     This  difficulty  caused  many  deaths.     The  per- 
centage of  males  from  the  first  cross  was  very  small. 
Among  forty-five  hybrids,  only  six  were  males.     Of  these 
three  died  at  birth,  one  died  in  less  than  twenty-four  hours 
after  birth,  one  proved  barren,  and  the  last  male  was 
killed  before  determining  his  fertility.     Charles  Good- 
night of  Texas  reports  2  that  "  no  male  calves  have  ever 
been  born;    cows  conceiving  them  either  suffer  abortion 
or  die,  hence  only  get  heifer  calves  and  only  a  small  per 
cent  of  them."    The  hybrids  produced  their  first  calves 
at  an  average  age  of  five  years  (Plate  XVII). 

1  Boyd,  Journal  of  Heredity,  1914,  p.  189. 

2  Goodnight,  Journal  of  Heredity,  1914,  p.  199. 


250  THE   BREEDING  OF  ANIMALS 

Three-quarter  blood  bisons  from  pure  bisons,  -bulls  and 
hybrid  cows  were  similar  in  form  and  color  to  the  bison ; 
one  cross-bred  from  a  half  Hereford  dam  had  a  white 
face.  One-quarter  blood  bisons  from  hybrid  dams  and 
Hereford  and  Aberdeen  Angus  bulls  were  uniform  in 
conformation  but  varied  in  color.  The  three-quarter 
bloods  closely  resembled  the  bison,  while  the  one-quarter 
bloods  could  not  readily  be  distinguished  from  domestic 
cattle.  From  twenty-four  hybrid  cows,  only  three  were 
regular  breeders  and  fifteen  were  barren.  From  twelve 
one-quarter  blood  bison  cows  bred  to  domestic  animals, 
seven  were  fully  fertile,  four  were  irregular  breeders,  and 
one  was  barren.  One  out  of  four  of  the  three-quarter 
blood  bison  cows  was  barren.  The  term  "  cattalo " 
is  used  by  Boyd  to  designate  the  third  generation.  When 
both  parents  are  of  mixed  blood,  the  cattaloes  are  in  many 
respects  superior  to  ordinary  domestic  cattle,  being  hardier 
and  much  less  subject  to  disease.  Cattaloes  with  a  high 
percentage  of  bison  blood  are  probably  immune  from 
Texas  fever  and  blackleg.  The  cattalo  grows  to  a  greater 
weight  than  domestic  cattle.  Goodnight 1  says,  "  More 
of  them  can  be  grazed  on  a  given  area.  They  do  not 
run  from  Heel  Flies  nor  drift  in  storms.  They  rise  on 
their  fore  feet  instead  of  their  hind  feet.  They  never 
lie  down  with  their  backs  down  hill,  so  they  are  able  to 
rise  quickly  and  easily." 

It  seems  entirely  probable  that  a  new  breed  will  be 
added  to  the  list  of  domestic  cattle,  and  if  this  result  is 
achieved,  it  will  be  one  of  the  very  few  authentic  cases  of 
the  establishment  of  a  new  breed  by  crossing  species. 

236.  The  mule  hybrid.  —  The  most  widely  distributed 
and  most  useful  hybrid  known  is  the  mule,  which  is  pro- 

1  Goodnight,  Journal  of  Heredity,  1914,  p.  199. 


CROSS-BREEDING  251 

duced  by  crossing  the  domestic  mare  to  the  jack.  In  1915 
there  were  4,479,000  mules  in  the  United  States.  This 
was  more  than  one-fifth  of  the  total  number  of  horses 
in  the  country  at  the  same  time.  The  production  of 
mules  has  increased  at  a  more  rapid  rate  than  horses,  and 
the  use  of  mules  is  becoming  more  extensive.  The  mule 
hybrid  is  a  remarkable  example  of  the  practical  advantages 
which  follow  a  particular  cross.  This  animal  is  more 
hardy  and  enduring  than  either  parent.  As  compared 
with  the  horse,  the  mule  is  longer-lived,  less  subject  to 
disease  or  injury,  and  more  efficient  in  the  use  of  food. 
The  mule  can  be  safety  put  to  work  at  a  younger  age,  will 
thrive  on  coarser  feed,  and  seems  to  be  much  better  able 
to  avoid  many  dangers  which  menace  the  usefulness  of 
the  horse.  The  mule  will  perform  more  arduous  labor 
on  less  food.  The  mule  will  endure  the  heat  of  southern 
latitudes  more  successfully  than  the  horse  and  is  there- 
fore a  popular  draft  animal  in  the  South. 

The  cross  between  the  mare  and  jack  is  readily  accom- 
plished and  the  union  is  perfectly  fertile.  The  conforma- 
tion of  the  mule  more  closely  resembles  that  of  his  sire. 
The  ears  are  long,  feet  long  and  narrow,  withers  sharp, 
mane  and  tail  scanty,  and  the  voice  a  bray  like  the  jack. 
The  mule  is  sterile.  A  few  cases  of  supposed  fertility  of 
mare  mules  have  been  reported,  but  the  writer  has  investi- 
gated several  apparently  reliable  reports  and  has  never 
found  an  authentic  case  of  a  fertile  mule.  Most  of  the 
erroneous  reports  of  fertile  mules  have  apparently  arisen 
from  the  not  infrequent  cases  of  mare  mules  which  have 
been  observed  suckling  mule  foals.  The  milk  glands  of 
mare  mules  have  been  known  to  function  as  the  result 
of  the  stimulation  afforded  by  a  suckling  foal.  A  case 
of  a  mare  mule  giving  milk  was  reported  to  the  writer 


252  THE   BREEDING   OF   ANIMALS 

by  L.  O.  Swarner  of  Boonville,  Missouri,  in  1913.  This 
mare  was  six  years  old  and  at  the  time  had  been  giving 
milk  for  five  weeks.  The  milk  glands  had  not  been  stimu- 
lated in  any  way,  but  the  milk  "  streamed  "  from  the 
udder.  It  is  also  of  interest  to  know  that  this  mare  mule 
showed  unmistakable  evidences  of  what  in  the  ordinary 
mare  would  be  regarded  as  complete  sexuality.  She 
came  in  heat  regularly.  The  mule  was  bred  frequently 
when  in  season  to  both  the  stallion  and  jack,  but  failed 
to  conceive.  A  sample  of  the  milk  was  analyzed  by  the 
Chemical  Department  and  found  to  contain  2.46  per  cent 
protein,  5.8  per  cent  sugar,  1.45  per  cent  fat,  and  .4  per 
cent  ash.  (See  Plate  III.) 

The  mare  mules  apparently  have  all  the  essential 
organs  of  reproduction  and  come  in  heat  with  considerable 
regularity.  The  horse  mule  also  has  the  essential  sexual 
organs  well  developed  and  his  sexual  instincts  are  so  well 
developed  that  castration  of  young  mules  is  universally 
practiced.  The  cause  of  sterility  in  the  horse  mule  is  not 
due  to  a  failure  to  develop  spermatozoa,  but  the  sperm- 
cells  are  imperfect.  In  some  cases  the  sperm-cells  lack 
the  tail  or  flagellum. 

237.  The  hinny  hybrid.  —  The  reciprocal  cross  between 
the   jennet   and   the   stallion   is   accomplished   without 
difficulty  and  the  union  is  very  fertile.     The  hybrid  from 
the  cross  is  called  a  hinny.     Some  authorities  have  held 
that  the  hinny  resembled  the  horse  much  more  closely 
than  the  mule,  but  this  is  denied  by  most  practical  breeders. 
The  hinny  is  not  commercially  important  as  the  jennet 
is  too  valuable  for  the  production  of  jacks  to  be  used  for 
crossing.    The  hinny  is  sterile.     (See  Plate  XVIII,  upper.) 

238.  Crossing  the  horse  and  the  zebra.  —  The  horse 
and   zebra  have  been  successfully  crossed  by  Ewart  of 


PLATE  XVIII.  —  Upper.       A    five-year-old   hinny.       Dam   a   jennet, 
sire  a  Percheron  stallion.     Lower.     Sheep-goat  hybrid. 


CROSS-BREEDING  253 

Edinburgh,  Scotland,  the  United  States  Department  of 
Agriculture  and  many  others.  The  zebra-horse  hybrid 
is  easily  domesticated  and  can  be  successfully  broken 
to  harness.  The  first  cross  is  not  so  easily  made  as  that 
between  the  jack  and  the  mare  but  is  not  impossible  or 
extremely  difficult.  The  zebra  possesses  a  much  smoother, 
finer  and  more  horse-like  form  than  the  ass,  and  the 
zebra  hybrid  therefore  is  possessed  of  more  quality  and 
"  finish "  than  the  mule.  This  hybrid  should  prove 
valuable,  particularly  in  those  regions  where  the  "  tsetse  " 
fly  is  fatal  to  horses  but  not  to  zebras  and  probably  not 
to  the  zebra  hybrids. 

239.  Crossing  cattle  and  zebu.  —  Many  crosses  have 
been  made  between  the  zebu  and  European  cattle  and 
between  the  zebu  and  the  cattle  of  Tunisia.  The  first 
cross  in  practically  all  of  the  experiments  seems  to  have 
been  successful. 

The  cross-bred  zebu  is  resistant  to  Texas  fever  and 
anthrax  and  is  not  seriously  inconvenienced  by  foot  and 
mouth  disease.1  In  Brazil  2  the  zebu  cross  is  popular. 
It  is  claimed  that  the  cross-bred  zebu  is  more  prolific  and 
that  these  animals  herd  together  better  than  the  ordinary 
domestic  cattle.  The  zebu  hybrids  are  less  tractable 
and  docile  than  domestic  cattle,  but  are  very  active  and 
enduring  draft  animals. 

Because  of  the  disease-resisting  qualities  of  the  zebu, 
its  prolificacy,  adaptability  to  hot  climates  and  general 
hardiness,  Nabours  3  is  of  the  opinion  that  this  type  of 
cattle  may  yet  become  an  important  breed  in  the  United 
States. 

1  Roederer,  Journal  of  Heredity,  1915,  p.  201. 

2  Hunnicutt,  Journal  of  Heredity,  1915,  p.  195. 

3  Nabours,  American  Breeder's  Magazine,  1913,  p.  38. 


254  THE   BREEDING   OF  ANIMALS 

240.  Sheep-goat  hybrid.  —  The  cross  between  the 
sheep  and  goat  has  been  successful  in  a  number  of  in- 
stances. Spillman  reports  such  a  hybrid  belonging  to  E. 
Armand  of  Monett,  Missouri.  (See  Plate  XVIII,  lower.) 

The  covering  of  the  body  of  this  hybrid  was  generally 
goat  hair,  but  the  back  was  covered  with  "  shaggy  wool." 
"  This  hybrid  is  a  female  and  appears  to  be  infertile,  but 
not  absolutely  so,  for  it  has  once  produced  a  half-grown 
foetus."  l 

1  Spillman,  Journal  of  Heredity,  1913,  p.  69. 


CHAPTER  XIII 
DEVELOPMENT 

THE  qualities  which  an  animal  possesses  are  due  in 
the  first  place  to  inheritance  and  in  the  second  place  to 
the  manner  in  which  the  inherited  qualities  have  been 
developed.  An  animal  cannot  develop  beyond  the  capaci- 
ties which  have  come  to  it  through  the  germ-plasm.  It 
is  also  true  that  the  capacities  which  are  inherited  cannot 
benefit  the  individual  unless  they  are  developed  through 
a  favorable  environment.  It  is  seldom  that  an  animal 
realizes  fully  the  possibilities  for  development  which  are 
inherent  in  the  germ-plasm.  The  carefully  bred  beef 
animal  inheriting  those  valuable  qualities  of  early  ma- 
turity, broad,  deep  and  rounded  form,  rugged  constitution 
and  quiet  temperament,  with  a  distinct  tendency  to  lay 
on  fat  when  food  is  abundant,  may  completely  fail  to 
exhibit  these  inborn  characters  and  actually  display  the 
form  and  characteristics  of  the  unimproved  animal  if  it 
has  been  surrounded  by  conditions  which  are  unfavor- 
able for  the  development  of  these  special  qualities.  The 
highly  improved  dairy  cow  with  the  inherited  capacity 
to  produce  enormous  quantities  of  milk  and  butter  may 
never  rise  above  mediocrity  if  she  is  not  supplied  with 
food  and  her  milking  functions  intelligently  developed. 
In  the  selection  of  animals  for  improvement,  the  skillful 
breeder  can  never  know  what  results  he  has  achieved 
until  the  products  of  his  skill  have  been  fully  developed. 

255 


256  THE   BREEDING   OF   ANIMALS 

It  is  not  too  much  to  say  that  no  man  can  be  a  successful 
breeder  who  is  not  also  skillful  in  developing  his  animals. 
Thus,  in  practice,  development  becomes  supremely  im- 
portant and  throughout  the  history  of  animal-breeding 
has  been  only  second  in  importance  to  heredity  itself. 
A  satisfactory  treatment  of  development  in  all  its  phases 
as  related  to  animal  husbandry  would  require  a  volume, 
and  as  the  chief  purpose  of  this  work  is  to  consider  how 
the  inherited  capacities  of  animals  fin  ally  appear  as  definite 
characters  in  the  germ-plasm,  only  a  limited  reference 
can  be  made  to  developmental  phases  of  chief  importance 
to  the  animal-breeder. 

241.  Growth.  —  From  the  fertilization  of  the  egg  until 
the  full  development  of  the  mature  individual,  the  animal 
increases  in  volume  and  changes  in  form.     This  increase 
and  change  of  form  is  called  growth.     The  final  size  of 
an  animal  is  determined  by  the  rate  of  growth  and  the 
length  of  the  growth  period.     The  guinea  pig  and  rabbit 
come  to  full  maturity  at  about  the  same  age,  but  the  rabbit 
is  larger  because  its  rate  of  growth  is  more  rapid.    The 
rate  of  growth  in  the  rabbit  and  man  is  about  equal, 
but  man  is  much  larger  at  maturity  because  the  period 
of  growth  is  much  longer.1 

242.  The  growth  impulse.  —  The  young  of  any  species 
tend  to  develop  and  grow  in  accordance  with  the  normal 
habit  of  the  species.     This  applies  in  a  special  sense  to 
the  skeletal  system.     Even  in  the  absence  of  a  sufficient 
supply  of  feed  and  other  favorable  conditions,  the  young 
animal  displays  a  remarkable  physiological  impulse  to 
continue  to  increase  in  the  skeletal  parts.     2  Animals  fed 

1  Morgan,  "Experimental  Zoology,"  p.  245. 

2  Waters,    "Capacity  of  Animals   to   Grow  under  Adverse 
Conditions." 


DEVELOPMENT  257 

on  a  limited  ration  will  continue  to  increase  in  height, 
length  of  body,  and  other  parts  of  the  skeleton,  at  the 
same  time  becoming  thinner  and  thinner  in  flesh.  Even 
during  starvation  the  same  tendency  is  apparent.  This 
fact  has  been  noted  by  H.  Aron,1  who  found  that  while 
fasting,  the  skeleton  grows  at  the  expense  of  the  other 
body  tissues. 

243.  Factors  influencing  growth.  —  The  chief  factors 
influencing  growth   in  the  domestic  animals   are  food, 
heat,    light,    age,    gestation    and    lactation.     The    chief 
condition  influencing  growth  in  normal  animals  is  the 
food  supply. 

244.  Growth  and  food  supply.  —  While  it  is  true  that 
the  animal  may  for  a  limited  time  add  to  its  tissues  when 
food  is  insufficient  in  either  quantity  or  quality,  it  is 
also  true  that  a  long-continued  deficiency  in  the  food 
supply  of  young  growing  animals  will  invariably  check 
their  growth.     The  check  to  growth  in  such  cases  may 
be  only  temporary,  or  it  may  result  in  permanently  decreas- 
ing the  normal  size  of  the  mature  animal.   (See  Plates  XIX 
and  XX.) 

245.  Capacity  to  grow.  —  The  young  animal  that  is 
stunted  as  a  result  of  insufficient  food  does  not  lose  the 
capacity  to  grow.    The  organism  seems  to  be  able  to 
continue  to  function  and  maintain  a  certain  equilibrium. 
If  later  a  greater  abundance  of  food  is  supplied,  the  rate 
of  growth  may  be  reestablished.     If  after  a  period  of 
partial  starvation  the  food  supply  is  abundant,  the  rate 
of  growth  may  for  a  time  be  even  more  rapid  than  before. 
That  the  capacity  of  an  animal  to  grow  is  not  destroyed 
by  stunting  is  shown  by  the  results  of  an  investigation 
at   the   Missouri   Experiment   Station    by  Waters  and 

1  H.  Aron,  Exp.  Sta.  Record,  vol.  24,  p.  765. 

s 


258  THE  BREEDING   OF  ANIMALS 

P.  F.  Trowbridge.1  These  investigators  fed  a  beef  steer 
from  the  age  of  three  months  to  thirty-eight  months  old. 
From  three  to  twelve  months  of  age  the  animal  was  fed 
on  a  maintenance  ration  (Plate  XXI).  An  attempt  was 
made  to  feed  the  young  calf  in  such  a  way  that  it  would 
neither  gain  nor  lose  in  live  weight.  At  the  beginning  of 
the  period  (three  months  old)  (Plate  XXI,  upper  left) 
the  animal  weighed  175  pounds;  at  twelve  months 
(Plate  XXI,  upper  right)  the  animal  weighed  212  pounds. 
Another  animal  similar  in  every  way  at  the  beginning 
was  fed  a  full  ration  of  nutritious  feed.  The  latter 
animal  increased  in  weight  from  200  pounds  at  four 
months  (see  Plate  IX)  to  875  pounds  at  336  days  of 
age  (Plate  VIII,  upper).  The  animal  fed  on  a  sparse 
ration  continued  to  increase  in  height,  length  of  body, 
size  of  bone,  and  other  skeletal  measurements  but  lost 
constantly  in  fat  and  gradually  became  leaner  and  thinner. 
At  the  end  of  the  twelve  months  the  steer  was  much 
emaciated  and  showed  symptoms  of  starvation.  From 
the  standpoint  of  the  practical  feeder,  the  animal  was 
clearly  stunted  in  its  growth,  and  in  the  opinion  of  many 
breeders  he  had  lost  very  greatly  in  his  capacity  to  gain 
in  live  weight  and  to  do  so  on  what  would  be  regarded  as 
a  normal  amount  of  food.  In  other  words,  his  economic 
value  for  the  production  of  beef  was  very  greatly  dimin- 
ished. After  twelve  months  the  animal  was  given  a 
gradually  increasing  amount  of  nutritious  food  until 
he  was  consuming  a  normal  ration.  The  animal  rapidly 
improved  in  condition  and  at  twenty-four  months  (Plate 
XXII)  had  reached  a  total  weight  of  1055  pounds,  a  total 
gain  of  842  pounds  in  twelve  months.  This  gain  was  not 
expensive  in  that  a  large  amount  of  feed  was  required  to 

1  Missouri  Experiment  Station,  unpublished  data. 


PLATE  XXI.  —  Starvation  does  not  destroy  capacity  to  grow.  Upper 
left.  Steer  529  weighing  175  pounds  at  age  96  days.  Ration  greatly 
restricted  until  age  365  days.  Upper  right.  Steer  529  weighing  only 
200  pounds  at  age  310  days.  Resulting  from  feeding  greatly  restricted 
ration.  Lower.  Same  animal  at  age  38  months  and  weighing  1487 
pounds. 


DEVELOPMENT  259 

produce  a  pound  of  gain,  but  on  the  other  hand  the  gain  in 
live  weight  was  accomplished  by  feeding  only  five  and  six 
one-hundredths  pounds  of  grain  and  two  and  four-tenths 
pounds  of  hay  for  each  pound  of  gain.  The  steer  that 
had  been  fed  generously  for  the  first  twelve  months  of 
its  life  gained  only  500  pounds  during  the  period  in 
which  the  stunted  one  had  gained  842  pounds.  In  the 
production  of  the  500  pounds  the  full-fed  steer  had  con- 
sumed nine  and  eight-tenths  pounds  of  grain  and  four 
and  two-tenths  pounds  of  hay  for  each  pound  of  gain  in 
live  weight.  Over  forty  per  cent  less  feed  was  required  by 
the  stunted  animal  for  each  pound  of  increase  in  live 
weight.  Not  only  did  the  stunted  animal  not  lose 
its  capacity  to  grow,  but  in  certain  respects  its  growth 
processes  were  accelerated  during  the  period  covered 
by  this  experiment  as  a  result  of  its  difficult  struggle 
for  existence  during  the  first  twelve  months  of  its 
life. 

246.  Growth  and  the  cell.  —  Increase  in  the  size  of 
animals  which  follows  growth  is  due  to  a  multiplication 
of  cells  and  not  to  an  increase  in  their  size.  The  size 
of  cells  varies  between  rather  narrow  limits.  The  larger 
size  of  some  animals  is  not  due  to  larger  cells  in  their 
organization  but  to  a  larger  number  of  cells.  It  is  also 
true  that  the  cells  in  any  individual  animal  vary  but 
little  in  size.  The  increase  in  size  of  any  part  of  an  animal 
is  due,  therefore,  to  an  increase  in  the  number  of  cells 
and  not  to  -an  expansion  of  cells  already  formed.  It  is 
true,  of  course,  that  certain  minor  exceptions  to  this  rule 
are  to  be  observed.  The  nerve  cells  vary  in  size  with  the 
size  of  the  animal.  The  nerve  cells  of  an  ox  are  much 
larger  than  those  of  the  pig.  The  frog  has  very  large 
cells,  while  the  starfish  is  composed  of  small  cells.  But 


260  THE  BREEDING  OF  ANIMALS 

a  large  frog  differs  from  a  small  frog  in  the  number  of 
cells,  not  in  their  size.  Each  individual  animal  begins  its 
existence  as  a  single  cell.  Through  cell  division  the  em- 
bryonic organism  rapidly  increases  in  size  until  maturity 
is  reached.  The  rate  of  growth  of  the  individual  is  most 
rapid  during  the  very  early  stages  in  the  development  of  the 
embryo.  The  rate  of  growth  decreases  gradually  from  this 
time  until  full  maturity,  when  nominally  growth  ceases. 

247.  When  the  growth  impulse  is  strongest.  —  The 
growth  impulse  is  strongest  in  the  animal  while  still  exist- 
ing in  the  uterus  of  the  mother.     After  birth  the  growth 
continues  less  rapidly,  but  is  still  very  rapid  when  compared 
with  the  increase  in  size  during  the  later  months  of  the 
growth  period.     It  is  for  this  reason  that  the  period  of 
gestation  is  so  fundamentally  important  in  the  life  of  the 
animal.     During  this  period  of  exceedingly  rapid  increase 
in  size  and  development  of  the  vital  organs  and  other  parts 
of  the  body,   any  abnormal  condition  which  interferes 
with  the  normal  requirements  of  the  unborn  animal  may 
cause  arrested  development  and  result  in  seriously  retard- 
ing the  growth  or  permanently  crippling  the  individual. 
It  is  undoubtedly  true  that  during  this  period  the  prac- 
tical breeder  may  through  skillful  feeding  and  care  ma- 
terially influence  for  good  or  evil  the  development  of  the 
valuable  characters  of  the  domestic  animals. 

248.  Development  of  the  foetus.  —  The  development 
of  the  fertilized  egg  through  the  embryonic  stages  of  the 
life  of  the  mammalian  animal  is  influenced  by  a  number 
of  conditions  which  may  have  a  profound  influence  upon 
the  material  well-being  of  the  future  mature  animal. 
Some  of  these  influences  are  as  yet  obscure  and  not  well 
understood,   while  others  are  more  clearly  determined 
and  their  effects  more  easily  recognized. 


DEVELOPMENT  261 

The  development  of  the  foetus  is  influenced  by  heredity, 
and  the  physiological  environment  of  the  pregnant  mother. 
Among  the  latter  are  the  general  health  or  well-being 
of  the  mother,  age,  the  quantity  and  quality  of  the  food 
supply  and  mental  impressions. 

249.  Heredity  and  foetal  development.  —  The  inherited 
tendencies  of  an  animal  are  exhibited  from  the  very  be- 
ginnings of  its  existence  in  the  fertilized  egg-cell.  Its  foetal 
development,  therefore,  must  be  influenced  to  a  certain 
extent  by  those  inherent  determiners  which  have  come  to 
the  fertilized  egg-cell  from  the  male  parent.  The  size  of 
the  foetus  at  various  stages  of  development  then  would  be 
determined,  not  alone  by  the  maternal  heredity  and  en- 
vironment, but  also  by  the  inherited  characteristics  which 
have  been  acquired  through  the  male.  At  the  same  time 
it  is  probable  that  the  maternal  environment  has  a  much 
more  important  influence  on  the  foetal  development  than 
its  paternal  hereditary  tendencies.  If  it  were  otherwise, 
serious  consequences  might  follow  the  mating  of  smaller 
females  to  much  larger  males  among  the  domestic  animals. 

Pony  mares  weighing  700  to  900  pounds  are  not  infre- 
quently mated  with  large  stallions  of  the  draft  breeds 
weighing  2000  pounds  or  more.  Under  these  conditions 
the  foetus  is  not  as  much  larger  than  the  normal  foetus 
of  the  mother  as  might  be  expected  from  the  much  greater 
size  of  the  stallion.  Small  burro  mares  weighing  400 
or  500  pounds  have  been  artificially  inseminated  with 
the  sperm  of  Percheron  and  other  heavy  draft  stallions. 
The  growth  of  the  foetus  in  this  case  is  undoubtedly  some- 
what greater  during  the  normal  period  of  gestation  than 
the  growth  of  a  pure  burro  foetus,  but  the  increased  size 
is  not  a  mean  between  the  normal  size  of  a  Percheron  and 
a  burro  foetus,  but  is  much  smaller. 


262 


THE   BREEDING   OF   ANIMALS 


RELATION  OF  WEIGHT  OF  DAM  TO  BIRTH  WEIGHT  OF 
LAMB 


WEIGHT  OP  DAMS 

NUMBER 

OP 

SINGLE 
LAMBS 

AVERAGE 
BIRTH 
WEIGHT 

OP 

SINGLE 
LAMBS 

NUMBER 
OF  TWIN 
LAMBS 

AVERAGE 
BIRTH 
WEIGHT 
OP  TWIN 
LAMBS 

AVERAGE 
BIRTH 
WEIGHT 
op  ALL 
LAMBS 

Below  90  Ibs.  .     . 

8 

7.2  Ibs. 



, 

7.2  Ibs. 

90  to  100  Ibs.      . 

6 

7.4  Ibs. 

— 

—  . 

7.4  Ibs. 

100  to  110  Ibs.      . 

14 

8.6  Ibs. 

8 

6.4  Ibs. 

7.5  Ibs. 

110  to  120  Ibs.      . 

12 

8.7  Ibs. 

20 

7.2  Ibs. 

7.9  Ibs. 

120  to  130  Ibs.      . 

13 

8.9  Ibs. 

10 

7.6  Ibs. 

8.3  Ibs. 

250.  Birth  weight  of  lambs.  —  The  author,1  investi- 
gating the  birth  weight  of  lambs  from  grade  Merino  ewes 
bred  successfully  to  Shropshire,  Hampshire  and  Merino 
rams,  found  that  the  size  of  lambs  at  birth  is  primarily 
determined  by  the  nutrition  of  the  foetus  while  carried 
in  the  uterus  of  the  mother.  The  nutrition  of  the  foetus 
will  of  course  be  determined  entirely  by  the  physiological 
condition  of  the  mother  during  gestation.  This  is  shown 
in  one  test  in  which  the  birth  weight  of  twenty-nine  lambs 
sired  by  two  heavy  rams  averaging  237  pounds  in  weight 
was  8.16  pounds.  The  average  weight  of  two  other 
rams  of  the  same  breeds  was  142J  pounds.  The  two 
lighter  rams  sired  twenty-five  lambs  from  the  same  ewes, 
or  ewes  of  the  same  type.  The  average  birth  weight  of 
these  lambs  was  8.75  pounds.  The  weight  of  the  sires 
in  this  case  seemed  to  have  little  influence  on  the  weight 
of  lambs  at  birth.  In  attempting  to  discover  the  real 
factors  determining  the  growth  of  the  foetus  as  measured 
by  the  weight  of  lambs  at  birth,  it  was  found  that  the 

1  F.  B.  Mumford,  "Some  Facts  Influencing  the  Weight  of 
Lambs  at  Birth,"  Bulletin  53,  Missouri  Experiment  Station. 


DEVELOPMENT  263 

nutritive  condition  and  weight  of  the  mothers  had  an 
important  influence  on  the  development  of  the  foetus. 
This  fact  is  shown  in  the  table  on  page  262. 

Summarizing  the  results  of  four  years'  work,  the  author 
says,1  "  We  must  conclude  from  the  exhibit  here  made, 
comprising  the  results  of  61  births,  that  the  weight  of 
the  mother  has  a  direct  influence  upon  the  birth  weight 
of  the  offspring  and  that  in  general  the  lambs  having  a 
heavier  weight  at  birth  are  produced  from  the  larger 
ewes." 

251.  Effect  of  protein  and  ash  in  ration  on  foetal 
development.  —  The  development  of  the  foetus  may  be 
materially  influenced  by  the  ration  given  to  the  mother 
during  pregnancy.  Evvard  1  has  shown  that  if  pregnant 
sows  are  fed  a  ration  poor  in  protein,  the  pigs  are  smaller 
at  birth.  Not  only  were  the  offspring  smaller  at  birth, 
but  they  were  weaker  and  the  death  rate  greater.  The 
first  investigation  was  made  with  young  sows  in  1910- 
1911.  These  were  fed  the  rations  indicated  in  the  table 
on  page  264  for  a  considerable  period.  The  results  are 
summarized  in  the  table. 

2  "  The  basal  ration  was  corn  alone.  Corn  we  know  is 
quite  deficient  in  protein  (the  zein  which  comprises  prac- 
tically 58  per  cent  of  said  protein  is  peculiarly  lacking  in 
two  quite  important  amino  acids,  namely,  tryptophane 
and  lysine)  and  calcium.  It  is  somewhat  surprising  to 
know  that  calcium  comprises  practically  two-thirds  as 
much  of  the  body  substance  as  does  nitrogen,  the  basal 
element  of  protein." 

"  Note  that  the  supplemented  rations  not  only  pro- 
duced larger  but  stronger  pigs  at  birth.  A  studied  survey 

1  Mumford,  loc.  cit.,  p.  176. 

2  Evvard,  Iowa  Academy  of  Science,  Report  1913,  p.  326. 


264 


THE  BREEDING   OF  ANIMALS 


of  the  above  figures  shows  most  clearly  that  even  though 
the  carbohydrates  were  limited,  as  in  the  meat  meal 
lots,  the  increase  in  protein  and  ash  was  such  as  to  mark- 
edly influence  the  size  and  strength  of  the  new-born  pigs. 
That  clover  and  alfalfa  should  also  have  a  marked  effect 
is  logical  because  these  hays  are  leguminous  in  character, 
run  high  in  protein  and  calcium,  and  also  have  an  alkaline 
ash  which  is  probably  beneficial." 

EFFECT  ON  OFFSPRING  OF  FEED  FED  PREGNANT  SWINE  l 
GILTS.— FIVE  IN  A  LOT,  1910-1911 


GILT  RECORD 

OFFSPRING  RECORD 

PREGNANCY  RATION 
op  GILTS 

Av.  Daily  Gain 
Lbs. 

Feed  Daily 

I 

?| 

*3 

>3 

< 

I.S 

^  8 

£S3 
* 

Per  cent  Vigor 

jjjj 

io  . 

V* 

H 

| 

I 

1 

0 
0 

0 
0 
3 

Corn  Only  .     .     . 
Corn+Meat  Meal 
(Light)    .     .     . 
Corn  +  Meat  Meal 
(Heavy)       .     . 
Corn  +  Clover  .     . 
Corn  +  Alfalfa  .     . 

.354 

.582 

.635 

.528 
.627 

3.65 
3.21 

2.75 
3.67 
3.74 

None 
0.127 

0.432 
0.302 
1.106 

7.6 
7.4 

8.8 
6.4 
7.6 

1.74 
2.01 

2.23 
2.21 
2.29 

68 
92 

93 
94 
89 

16 
5 

5 
0 

8 

16 
3 

2 
6 
0 

A  similar  test  with  older  (yearling)  sows  confirmed  the 
conclusions  from  the  first  investigation.  In  the  latter 
trial  there  was  evidence  that  animal  protein  supplied  in 
meat  meal  was  more  efficient  than  vegetable  protein 
supplied  in  linseed  oil  meal. 

252.  High  calcium  rations  for  pregnant  swine.  —  The 
ordinary  rations  fed  to  farm  animals  in  most  localities 

1  Evvard,  Iowa  Academy  of  Science,  Report  1913,  p.  326. 


DEVELOPMENT  265 

are  known  to  be  deficient  in  calcium.  This  is  particu- 
larly true  when,  as  in  the  case  of  swine,  the  rations  are 
chiefly  composed  of  grain  with  a  relatively  small  propor- 
tion of  roughage.  It  is  a  popular  notion  that  feeding 
pregnant  farm  animals  a  high  calcium  ration  will  cause 
the  skeletal  system  of  the  foetus  to  develop  even  beyond 
what  may  be  regarded  as  normal.  As  a  result  of  this 
greater  development  of  the  skeleton,  it  has  been  alleged 
that  the  mother  may  sometimes  have  serious  difficulty 
in  expelling  the  foetus.  Sbme  confirmation  of  this  belief 
is  apparently  found  in  the  work  of  Evvard  already  de- 
scribed. But  in  this  investigator's  trials  a  ration  abnor- 
mally deficient  in  calcium  and  protein  is  compared  with 
normal  rations.  Adding  an  excess  of  calcium  to  a  normal 
ration  may  not  necessarily  increase  the  size  or  change  the 
composition  of  the  foetus.  In  this  respect  we  know  that 
similar  changes  in  the  ration  do  not  change  the  composi- 
tion of  the  milk.  At  the  Wisconsin  Experiment  Station, l 
Hart,  Steenbock  and  Fuller  compared  normal  rations 
with  a  high  calcium  ration  fed  to  pregnant  swine.  Eight 
Poland  China  sows  were  fed  in  lots  of  two  each.  Three 
lots  were  fed  on  a  high  calcium  ration  by  the  addition  of 
calcium  carbonate,  calcium  phosphate  (floats)  and  alfalfa. 
One  lot  was  fed  a  normal  standard  ration  known  to  be 
adequate  for  pregnant  swine.  These  rations  were  fed 
throughout  the  gestation  period.  Although  the  calcium 
rations  contained  five  times  the  amount  of  this  mineral 
present  in  the  normal  ration,  there  was  no  evidence 
that  the  skeleton  of  the  foetus  was  influenced  in 
any  degree.  The  authors  in  summarizing  their  results 

1  Hart,  Steenbock  and  Fuller,  "  Calcium  and  Phosphorus 
Supply  of  Farm  Feeds  and  their  Relation  to  the  Animal's  Re- 
quirements," Wisconsin  Research  Bulletin  No.  30. 


266         .       THE  BREEDING   OF  ANIMALS 

conclude  that  "  High  calcium  rations,  as  compared  with 
low  calcium  rations,  had  no  effect  whatever  during  a 
single  gestation  period  on  the  size  or  calcium  content  of 
the  skeleton  of  the  foetus.  The  skeleton  is  not  increased 
in  any  dimension  by  a  wide  variation  in  the  amount  of 
calcium  fed  the  mother." 

253.  Size  and  vigor  of  foetus  as  influenced  by  corn  and 
wheat  rations.  —  The  particular  rations  fed  to  breeding 
animals  may  profoundly  influence  the  character  of  the 
foetus.  It  is  not  enough  that  the  prospective  mother 
should  receive  a  ration  containing  the  right  proportions 
of  protein,  carbohydrate  and  mineral  substances,  but 
these  minerals  must  be  of  the  kind  of  substances  which 
are  known  to  satisfy  the  nutritive  necessities  of  the  ani- 
mal. A  most  interesting  demonstration  of  this  fact  was 
made  possible  through  the  valuable  work  of  Hart,1  McCol- 
lum,  Steenbock  and  Humphrey  at  the  Wisconsin  Experi- 
ment Station.  In  May,  1907,  these  investigators  began 
feeding  four  heifers  a  ration  of  corn  meal,  corn  stover  and 
gluten  feed,  all  corn  products.  Another  group  of  four 
was  fed  wheat  meal,  wheat  straw  and  wheat  gluten,  nutri- 
ents derived  entirely  from  the  wheat  plant.  The  mate- 
rials supplied  in  each  ration  were  proportioned  in  such  a 
manner  as  to  furnish  each  group  of  animals  a  well- 
balanced  ration  in  accordance  with  the  accepted  feeding 
standards.  The  feeding  continued  for  two  years  and 
accurate  records  were  kept  of  feed  consumed,  gains  in 
live  weight,  and  physiological  condition  of  all  animals  in 
the  experiment. 

1  Hart,  McCollum,  Steenbock  and  Humphrey,  "Physio- 
logical Effect  on  Growth  and  Reproduction  of  Rations  Balanced 
from  Restricted  Sources,"  Research  Bulletin  No.  17,  Wisconsin 
Experiment  Station. 


PLATE  XXIII.  —  Upper.  A  normal  healthy  cow  in  good  nutritive 
condition  fed  exclusively  on  nutrients  derived  from  Indian  corn. 
Lower.  This  vigorous,  thrifty,  well-developed  new-born  calf  from  dam 
(upper)  fed  exclusively  corn  ration  before  and  during  gestation. 


PLATE  XXIV.  —  Upper.  Unthrifty  cow  clearly  in  bad  nutritive  con- 
dition due  to  having  been  fed  wheat  products  exclusively.  Lower.  Calf 
of  low  vitality  from  dam  (upper)  fed  exclusively  on  wheat  products, 
lived  only  twelve  hours. 


DEVELOPMENT  267 

The  rate  of  growth  of  all  animals  in  the  two  groups 
was  very  similar,  indicating  little  difference  in  the  effi- 
ciency of  the  rations.  But  that  there  was  a  difference 
is  indicated  by  the  author's  description  : 1  "  The  corn-fed 
animals  (Plate  XXIII)  looked  smooth  of  coat,  fuller  through 
the  barrel ;  and,  as  expressed  by  experienced  feeders  and 
judges  of  domestic  animals,  they  were  in  a  better  state  of 
nutrition.  On  the  other  extreme  stood  the  wheat-fed 
group  with  rough  coats,  gaunt  and  thin  in  appearance, 
small  of  girth  and  barrel,  and  to  the  practical  eye,  in  rather 
a  lower  state  of  nutrition."  But  perhaps  the  most  sig- 
nificant results  of  this  experiment  were  the  effects  of  these 
rations  on  the  reproductive  functions  of  the  mothers  and 
the  vitality  of  the  offspring.  The  gestation  period  in  the 
corn-fed  mothers  was  practically  normal,  while  in  every 
case  the  calves  of  the  wheat-fed  group  were  dropped 
from  two  to  five  weeks  before  the  end  of  the  normal 
gestation  period.  The  calves  from  the  corn-fed  cows 
were  uniformly  strong  and  vigorous  and  were  normal 
in  every  respect.  The  calves  from  the  wheat-fed  cows 
were  all  born  dead  or  with  such  low  vitality  that  they 
soon  died. 

The  yield  of  milk  from  the  wheat-fed  (Plate  XXIV) 
cows  was  distinctly  below  that  of  the  corn-fed  group.  In 
discussing  the  significant  results  of  this  investigation  the 
authors  say,  "  These  results  emphatically  show  how  de- 
pressing or  stimulating  the  influence  of  a  ration  may  become, 
even  when  it  is  made  up  of  supposedly  normal  feed  materials 
and  balanced  as  to  ordinary  chemical  constituents  and 
supply  of  energy,  especially  when  that  ration  is  continued 
for  a  long  time.  The  evidence  for  the  necessity  of  giving 
much  weight  to  the  physiological  influence  of  the  ration, 
1  Loc.  cit. 


268  THE   BREEDING  OF  ANIMALS 

apart  from  its  digestible  protein  content  and  calorific 
value,  is  positive." 

254.  The  permanent  effect  of  retarded  growth.  —  Is 
the  retardation  of  growth  resulting  from  unfavorable 
environment  a  permanent  condition?  Is  it  possible  per- 
manently to  stunt  an  animal?  This  question  is  one  of 
great  interest  to  the  practical  breeder  of  live-stock  and 
the  live-stock  farmer.  The  animal  is  often  employed  by 
the  farmer  for  the  purpose  of  disposing  profitably  of  food 
materials  which  are  of  limited  value  from  the  standpoint 
of  nutrients  and  digestibility,  but  nevertheless  have  a 
food  value.  Teachers  and  investigators  in  animal  hus- 
bandry have  for  a  long  time  taught  that  any  condition 
which  resulted  in  stunting  the  young  animal,  perma- 
nently affected  the  mature  individual.  It  has  also  been 
claimed  by  some  that  the  capacity  to  grow  was  materially 
diminished  by  a  stunting  period. 

The  history  of  two  animals  which  were  fed  at  the 
Missouri  Experiment  Station  by  P.  F.  Trowbridge1  is  of 
great  interest  in  attempting  to  answer  this  question.  One 
of  these  animals  was  given  a  full  ration  from  birth  and 
the  other  animal  was  given  a  so-called  maintenance  ration 
from  three  months  of  age  to  thirteen  months.  The  use 
of  the  term  maintenance  ration  in  this  connection  means 
that  it  was  planned  to  feed  the  animal  sufficient  food  to 
cause  it  to  maintain  a  uniform  body  weight.  As  a  matter 
of  fact,  the  animal  added  somewhat  to  his  total  weight 
in  the  ten  months  of  stunting.  The  tables  and  pictures 
(Plate  XXV)  give  a  very  clear  idea  of  the  general  results 
of  this  trial.  The  full-fed  animal  gained  rapidly  and  at 
the  end  of  fourteen  months  weighed  956  pounds.  The 
young  animal  fed  merely  a  maintenance  ration  weighed 

1  Missouri  Experiment  Station,  unpublished  data. 


PLATE  XXV.  —  Permanent  effect  of  retarded  growth.  The  animal  on  the 
left  (No.  527)  was  fed  the  maximum  amount  of  a  nutritious  ration  from  birth. 
The  animal  on  the  right  (No.  529)  was  starved  until  twelve  months  of  age 
and  then  fed  generously  to  age  thirty-eight  months.  See  table  on  page  269. 


DEVELOPMENT 


269 


only  207  pounds  at  the  age  of  thirteen  months.  At  that 
time,  the  animal  was  emaciated  in  appearance,  showed 
every  symptom  of  starvation,  and  was  to  all  appearances 
very  severely  stunted  in  its  growth  and  development. 
From  twelve  months  to  thirty-eight  months,  the  animal 
fed  previously  on  a  maintenance  ration  was  later  given  a 
generous  ration  and  gained  during  that  period  a  total  of 
1280  pounds.  The  full-fed  animal  during  the  same  period 
gained  853  pounds.  At  the  end  of  the  period  the  animal 
that  was  stunted  during  its  early  life  was  over  300  pounds 
lighter,  was  apparently  somewhat  shorter,  with  finer  bones, 
than  the  full-fed  animal.  There  was  little  doubt  but  that 
in  this  trial  the  early  environment  permanently  decreased 
the*  size  of  the  adult  animal. 

255.  Early  stunting  and  the  capacity  to  grow.  —  It  is 
interesting  to  know  that  the  capacity  to  grow  was  not 

THE  PERMANENT  EFFECTS  OF  RETARDED  GROWTH 
Feed  and  Weight  Records  of  Two  Steers  for  24  Months 

No.  527  was  fed  a  generous  ration  until  38  months  of 
age.  No.  529  was  starved  for  the  first  12  months  and 
then  given  a  full  ration  until  38  months  of  age. 


AGE  1  TO  12  Mos. 

AGE  12  TO  18  Mos. 

AGE  12  TO  24  Mos. 

No.  527 

No.  529 

No.  527 

No.  529 

No.  527 

No.  529 

Initial  Weight  (Ibs.) 

165.0 

175.0 

901.8 

213.5 

901.8 

213.5 

Final  Weight  (Ibs.) 

901.8 

213.5 

1178.2 

694.9 

1401.7 

1054.7 

Gain  during  Period 

736.8 

38.5 

276.4 

481.40 

499.9 

841.2 

Av.  Daily  Gain  .     . 

2.046 

0.106 

1.535 

2.674 

1.388 

2.336 

Grain  Fed  Daily     . 

6.926 

0.571 

14.686 

10.030 

13.610 

11.829 

Hay  Fed  Daily  .     . 

3.578 

0.895 

6.401 

4.840 

5.821 

5.642 

Grain  per  Lb.  Gain 

3.384 

5.343 

9.560 

3.750 

9.801 

5.062 

Hay  per  Lb.  of  Gain 

1.748 

8.370 

4.168 

1.813 

4.191 

2.415 

Total  Grain  Eaten 

2493.44 

205.73 

2643.48 

1805.50 

4899.86 

4258.55 

Total  Hay  Eaten    . 

1288.12 

322.53 

1152.18 

872.83 

2095.58 

2031.13 

270 


THE   BREEDING   OF   ANIMALS 


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DEVELOPMENT  271 

destroyed  by  the  early  stunting  resulting  from  insuffi- 
cient food.  The  gains,  the  amount  of  food  consumed, 
and  the  gain  in  live  weight  based  on  each  pound  of 
grain  consumed  is  shown  in  the  tables  for  the  various 
periods  of  the  feeding  experiment.  (Tables  on  pages 
269,  270.)  It  will  be  observed  from  the  figures  given 
in  these  tables  that  the  animal  subjected  to  severe  condi- 
tions of  feeding  during  its  early  life  evidently  had  a 
greater  capacity  for  growth,  and  made  better  use  of  the 
food  consumed,  than  did  the  animal  that  received  a 
generous  ration  during  the  same  period  of  its  life. 
There  can  be  no  question  but  that  under  certain  con- 
ditions a  significant  check  to  the  development  of  an 
animal  may  actually  increase  the  rate  of  growth  during 
the  later  periods  of  its  life. 

256.  Climate.  —  Small  animals  like  mice  and  domestic 
rabbits   reared   in   artificially   heated    temperatures   are 
noticeably  larger  than  normal  size  and  have  less  hair  on 
the  bodies.     Cattle  that  are  well  fed  and  housed  in  warm 
barns  have  much  less  hair  than  animals  of  similar  breed- 
ing that  are  required  to  live  exposed  to  the  rigors  of  severe 
cold  weather. 

257.  The  age  factor  in  animal-breeding.  —  Very  large 
numbers  of  farm  animals  are  bred  and  produce  offspring 
while  still  immature.     The  use  of  young  sires  among 
all  classes  of  animals  is  general,  but  especially  is  their  use 
common   in   the    breeding    of    hogs,    sheep   and   cattle. 
Various  opinions  exist  among  breeders  as  to  the  good  or 
evil  effects  which  follow  this  practice.     Some  of  the  evil 
results  which  it  is  claimed  have  followed  the  long-con- 
tinued mating  of  immature  animals  are,  a  gradual  decrease, 
in  the  size  of  the  breed ;   weakness  of  constitution ;   loss 
of  prepotency  in  the  transmission  of  valuable  qualities; 


272  THE  BREEDING  OF  ANIMALS 

a  retardation  of  the  growth  of  the  young  parents  and,  in 
some  cases,  a  permanent  dwarfing  of  the  mother. 

The  supposed  evil  results  following  premature  preg- 
nancy must  result  either  from  variations  produced  in  the 
fundamental  constitution  of  the  germ-plasm  or  in  changes 
in  the  soma-  or  body-cells.  Those  breeders  who  contend 
that  long-continued  breeding  of  immature  animals  results 
in  actually  decreasing  the  size  of  the  race  or  breed  believe 
that  the  real  character  of  the  breed  has  been  changed,  and 
changed  in  such  a  way  that  the  individuals  of  the  breed 
are  no  longer  able  to  produce  offspring  which  possess  the 
capacity  to  develop  into  animals  of  the  recognized  stand- 
ard size  of  the  breed.  They  would  insist  that  the  funda- 
mental nature  of  the  breed  has  been  changed  in  such  a 
way  as  permanently  to  affect  their  hereditary  character. 
It  is  obvious  that  if  this  contention  of  breeders  is  correct, 
it  is  contrary  to  our  present  ideas  of  the  inheritance  of 
acquired  characters.  Biologists  generally  would  first 
insist  on  a  more  accurate  demonstration  of  the  alleged 
fact  that  the  size  of  the  breed  is  actually  diminished  as  a 
result  of  early  pregnancy  and  lactation.  If  it  should 
be  found  that  this  practice  has  apparently  resulted  in  a 
smaller  breed,  the  biologist  would  undertake  to  explain 
the  observed  fact  on  different  grounds. 

258.  Premature  breeding  decreases  size.  —  First,  is  it 
true  that  premature  breeding  has  ever  resulted  in  decreas- 
ing the  size  of  the  breed  ?  It  must  be  admitted  that 
experienced  breeders  are  very  often  accurate  observers. 
Investigators  who  disregard  the  facts  which  have  been 
determined  by  practical  breeders  through  a  long  period 
of  successful  experience  are  neglecting  a  valuable  source 
of  knowledge  on  many  of  the  complex  problems  of  heredity 
and  development.  That  breeders  have  observed  that  long- 


DEVELOPMENT  273 

continued  early  breeding  results  in  decreasing  the  size 
of  the  breed  is  indicated  from  an  investigation  made  by 
J.  M.  Jones  under  the  writer's  direction  in  1912.  Spe- 
cific questions  were  formulated  and  sent  to  a  large  number 
of  successful  breeders  in  America  and  Great  Britain. 
From  these  replies  it  was  determined  that  216  breeders 
had  observed  that  early  mating  resulted  in  weakening 
the  breed,  diminishing  the  fecundity,  and  decreasing  the 
size.  That  such  results  followed  was  denied  by  thirty-five 
breeders.  Of  the  total  number  replying,  158  believed 
that  the  size  was  decreased  but  that  fecundity  was  not 
diminished.  It  is  very  clear  from  the  statistics  presented 
and  from  the  extended  replies  of  the  intelligent  breeders 
that  under  certain  conditions  the  size  of  the  animals 
comprising  the  herd  of  a  breeder  who  continually  breeds 
his  animals  prematurely  is  smaller  than  the  size  of  ani- 
mals in  the  herds  of  breeders  who  cause  their  animals  to 
mate  at  a  more  mature  age. 

259.  Decreased  size  due  to  early  breeding  not  in- 
herited. —  In  recognizing  the  fact  that  premature  breeding 
does  decrease  the  size  of  the  breed  under  certain  condi- 
tions, it  is  not  necessary  for  us  to  assume  that  the  tend- 
ency to  decreased  size  in  this  case  is  inherited.  Early 
breeding  can  have  no  direct  influence  in  changing  the 
fundamental  constitution  of  the  germ-plasm.  It  cannot, 
therefore,  change  the  general  prepotency  of  the  breed 
in  transmitting  the  recognized  standard  qualities  of  the 
race.  ,We  must  therefore  look  for  an  explanation  outside 
of  the  supposed  influence  on  the  hereditary  powers  of  the 
breed.  The  real  effects  from  premature  mating  are  to 
be  found  in  the  development  of  the  individuals  as  affected 
by  environment.  The  effects  of  gestation  and  lactation, 
if  observable  at*  all,  would  be  exhibited  in  the  young  par- 


274  THE  BREEDING  OF  ANIMALS 

ents  or  their  offspring,  or  in  permanent  effects  on  the  race 
or  breed.     It  might,  in  fact,  influence  all  three. 

260.  Influence  of  early  pregnancy  on  the  mother.  - 
The  chief  harmful  effect  which  follows  the  mating  of 
immature  breeding  animals  is  a  retardation  or  sudden 
check  to  the  growth  of  the  young  mother.  Investigation 
shows  that  the  premature  exercise  of  the  breeding  func- 
tions in  the  young  female  acts  in  some  instances  as  a 
temporary  inhibitor  of  growth.  The  author  has  for  six 
years  compared  the  growth  of  immature  mothers  with  the 
normal  growth  curves  of  mothers  mated  when  more 
mature.  In  this  investigation  six  Duroc  Jersey  sows  were 
divided  into  three  groups.  These  groups  of  two  sows 
each  were  designated  respectively  as  immature,  half 
mature  and  mature.  The  sows  of  the  immature  group 
were  bred  at  the  beginning  of  puberty  or  at  the  first  heat. 
At  this  early  period  the  young  mother  was  very  imma- 
ture. The  half  mature  sows  were  bred  at  about  eighteen 
months  and  the  mature  sows  at  about  thirty  months  of 
age.  Careful  records  of  the  food  consumed,  the  gain  in 
live  weight,  and  increase  in  body  measurements  were  made 
of  each  animal  in  the  experiment.  Similar  records  were 
made  of  the  female  offspring  of  the  original  sows  for  sev- 
eral generations.  The  body  measurements  were  taken 
with  a  view  to  determining  muscular  and  skeletal  increase. 
A  large  number  of  measurements  was  made,  and  these 
clearly  demonstrated  the  fact  that  the  early  exercise  of 
the  breeding  function  in  swine  results  in  temporarily 
checking  the  growth  of  the  mother.  The  investigations 
have  progressed  far  enough  at  this  time  to  measure  also 
the  ultimate  effect  upon  the  mature  mother.  While 
the  observations  have  not  yet  included  enough  animals 
to  justify  us  in  speaking  with  finality,  yet  it  seems  entirely 


DEVELOPMENT 


275 


safe  to  conclude  that  under  certain  conditions  premature 
breeding  results  in  a  permanent  reduction  in  the  normal 
size  of  the  mother.  Young  sows  which  have  been  bred 
at~the  beginning  of  puberty  and  twice  a  year  thereafter 
until  full  maturity  have  in  every  case  been  smaller  at 
maturity  than  sows  in  the  half  mature  and  mature  groups. 

RETARDATION  OF  GROWTH  DUE  TO  PREMATURE  BRE-EDING 
OF  Sows 

Measurements  taken  at  42  months  of  age 


LENGTH  OP 

HEART 

HEIGHT  AT 

DEPTH  OP 

BODY 

GIRTH 

WITHERS 

CHEST 

Centimeters 

Centimeters 

Centimeters 

Centimeters 

Immature1    . 

106 

125 

65 

41 

(Factor  6) 

Half  Mature  2     .     . 

124 

142 

70 

47 

(Factor  3) 

Mature3    .... 

116 

152 

71 

49 

(Factor  8) 

In  the  above  table  are  recorded  the  more  important 
measurements  of  a  typical  representative  of  each  of  the 
three  groups.  It  will  be  observed  that  at  forty-two  months 
of  age  the  immature  sow  was  materially  smaller  m  length 
of  body,  height  at  withers,  depth  of  chest,  and  in  heart 
girth.  At  this  age  (three-and-one-half  years)  the  young 
sow  had  produced  thirty-nine  pigs  in  five  litters,  the  half 
mature  sow  sixteen  pigs  in  two  litters,  and  the  mature 
sow  eight  pigs  in  one  litter.  But  one  conclusion  is  possible 

1  Has  produced  5  litters  and  a  total  of  39  pigs. 

2  Has  produced  2  litters  and  a  total  of  16  pigs. 

3  Has  produced  1  litter  and  a  total  of  8  pigs. 


276 


THE  BREEDING   OF   ANIMALS 


from  these  results,  that  early  pregnancy  and  lactation 
does  retard  the  growth  of  the  young  mother. 


RETARDATION  OP  GROWTH  DUE  TO  PREMATURE 
BREEDING 

Measurements  taken  at  maturity  —  66  months  of  age 


LENGTH  OP 

HEART 

WEIGHT  AT 

DEPTH  OF 

BODY 

GIRTH 

WITHERS 

CHEST 

Centimeters 

Centimeters 

Centimeters 

Centimeters 

Immature1     .     .     . 

108 

123 

66 

40 

(Factor  6) 

Half  Mature2     .     . 

120 

127 

67 

44 

(Factor  3) 

Mature3    .... 

118 

143 

71 

48 

(Factor  8) 

In  the  above  table  the  measurements  of  the  same 
animals  at  full  maturity  are  shown.  At  the  time  these 
measurements  were  taken  the  parents  were  about  five-and- 
one-half  years  of  age.  The  sow  that  was  mated  at  the  be- 
ginning of  puberty  and  bred  regularly  thereafter,  produc- 
ing sixty-nine  pigs  in  nine  litters,  was  smaller  at  maturity 
than  either  of  the  other  groups  which  were  mated  at  an 
older  age.  This  result  has  been  secured  in  a  number  of 
similar  cases.  In  other  words,  the  breeding  of  sows  at  a 
young  age  not  only  results  in  a  temporary  check  to  their 
development,  but  tends  permanently  to  decrease  the  size. 
This  permanent  decrease  is  not  very  marked  and  practi- 
cally may  not  be  of  great  importance.  It  is  clear  from  the 

1  Has  produced  9  litters  and  a  total  of  69  pigs. 

2  Has  produced  6  litters  and  a  total  of  49  pigs. 

3  Has  produced  5  litters  and  a  total  of  32  pigs. 


DEVELOPMENT  277 

records  that  one  important  practical  result  of  early  mating 
is  that  by  following  this  practice  a  much  larger  number 
of  young  are  produced  during  the  lifetime  of  the  parent. 
In  producing  hogs  commercially,  this  advantage  might 
easily  overcome  any  disadvantage  arising  from  a  reduc- 
tion in  the  size  of  the  mother. 

261.  Gestation  and  lactation  in  relation  to  growth.  — 
The  two  most  important  phenomena  associated  with 
reproduction  which  might  have  a  measurable  influence  on 
growth  are  gestation  and  lactation.  The  period  of  gesta- 
tion in  the  mammalian  domestic  animals  is  the  period  dur- 
ing which  the  embryo  is  developing  in  the  uterus,  from 
the  fertilization  of  the  egg  until  the  young  animal  is 
sufficiently  matured  to  carry  on  an  independent  existence 
outside  the  body  of  the  mother.  During  this  period  the 
unborn  animal  increases  rapidly  in  size,  and  within  its 
tissues  the  processes  of  cell  division,  absorption  and 
assimilation  proceed  with  exceptional  energy.  The  nutri- 
tion for  the  growth  of  the  foetus  during  this  period  is 
supplied  entirely  by  the  pregnant  mother.  The  foetus 
itself  has  no  means  of  nourishing  its  own  tissues.  It  is 
wholly  dependent  upon  the  mother.  To  all  intents 
and  purposes  the  young  animal  in  the  uterus  is  an  organic 
part  of  the  body  of  the  mother.  The  foetus  is  an  enormous 
parasite  nourished  by  the  mother  through  the  circulation. 

It  is  a  popular  opinion  among  many  breeders  tliat 
gestation  is  an  exhaustive  period  for  the  mother,  that 
during  this  period  the  mother  must  not  only  provide  for 
her  own  physiological  needs,  but  in  addition  must  supply 
the  materials  needed  for  the  rapid  development  of  the 
foetus.  It  has  been  generally  believed  that  because  of 
these  facts  the  period  of  gestation  is  a  severe  strain  on  the 
pregnant  mother.  If  the  mother  herself  has  completed 


278  THE   BREEDING   OF  ANIMALS 

her  growth  or  has  approached  maturity  in  her  develop- 
ment, the  changes  which  take  place  in  her  organization 
and  which  may  be  due  to  her  pregnant  condition  will 
obviously  not  affect  her  growth.  On  the  other  hand,  if 
the  mother  is  young  and  growing  rapidly,  gestation 
might  act  as  a  check  to  growth  if  the  physiological  pro- 
cesses of  the  mother  are  necessarily  and  chiefly  directed 
toward  the  development  of  the  foetus.  The  physiological 
processes  concerned  in  the  nutrition  of  the  foetus  are 
somewhat  complex  and  the  interrelations  between  the 
mother  and  her  unborn  young  not  completely  deter- 
mined. The  information  available  on  the  subject  does 
not  specifically  answer  the  question.  We  know  that  the 
absorption  of  fats  from  the  intestine  proceeds  at  a  more 
rapid  rate  during  pregnancy.  Increased  amounts  of  fat 
in  the  liver  cells  also  are  associated  with  pregnancy. 

There  is  a  tendency  to  increase  in  body  weight  during 
gestation.  The  maternal  body  increases  in  weight 
independently  of  the  increase  in  size  of  the  foetus  and 
foetal  membranes  as  shown  by  Gassner 1  and  confirmed 
by  others.  This  increase  in  weight  is  common  to  the 
mature  pregnant  mammalian  mother  and  is  not  confined 
to  the  young  parent  only.  It  is  possible,  therefore,  that 
this  increase  might  be  due  to  increased  fat  in  the  body 
and  not  to  any  increase  in  the  skeleton.  If  this  were 
found  to  be  true,  it  would  tend  to  confirm  current  opinion 
as  to  the  retarding  influence  of  gestation  on  the  growth. 

262.  The  Missouri  experiments.  —  At  the  Missouri 
Experiment  Station 2  careful  measurements  have  been 
made  of  a  large  number  of  immature  pregnant  sows  and 

1  Marshall,  "Physiology  of  Reproduction,"  chap.  XI. 

2  Mumford,    Bulletins    131    and    141,   Missouri    Experiment 
Station. 


DEVELOPMENT  279 

of  sows  not  pregnant  for  the  purpose  of  answering,  if 
possible,  the  question  whether  gestation  is  a  period  of 
such  severe  physiological  strain  on  the  young  mother 
that  it  stops  normal  growth.  A  large  number  of  animals 
have  been  under  observation  in  this  experiment  and  the 
results  are  fairly  uniform.  Measurements  included  rec- 
ords of  changes  in  body  weight,  heart  girth,  length  of 
body,  height  at  withers,  and  other  measurements. 

The  investigation  is  not  complete,  and  further  work 
may  modify  the  conclusions  which  seem  fully  warranted 
at  this  time.  The  results  so  far  justify  the  following 
conclusions : 

1.  The   exercise   of  the   reproductive  functions,   con- 
tinuously from  the  beginning  of  puberty  to  full  maturity, 
permanently  decreases  the  normal  adult  size  of  the  mother. 

2.  This  permanent  effect  on  the  size  of  the  mother 
occurs  even  under  a  favorable  environment. 

3.  The  period  of  gestation  is  not  a  check  to  growth 
when  a  full  ration  of  nutritious  food  is  supplied.     The 
rate  of  growth  is  not  lessened  during  gestation.     There 
is  some  evidence  that  pregnancy  is  an  actual  stimulus  to 
growth. 

4.  The  period  of  lactation  is  a  very  severe  physiological 
strain  on  the  young  mother,  and  during  this  period  growth 
is  apparently  inhibited. 

5.  After  the  end  of  lactation  or  when  the  young  are 
weaned,  the  rate  of  growth  in  the  young  mother  is  more 
rapid  than  before  pregnancy  and  more  rapid  than  in 
animals  which  have  not  been  pregnant. 


CHAPTER  XIV 
THE  PRACTICE  OF  BREEDING 

IF  the  modern  breeds  of  domestic  animals  are  com- 
pared with  the  original  unimproved  forms,  remarkable 
differences  will  be  observed.  In  many  of  the  characters 
which  have  come  to  be  of  inestimable  value  to  man,  the 
modern  animal  is  notably  superior  to  the  original  unim- 
proved forms.  And  in  other  characters,  less  substantial 
and  economically  significant,  modifications  of  great  scien- 
tific interest  have  resulted  from  systematic  selection  by 
man. 

263.  Improvement  in  size.  —  For  many  purposes  the 
wild  unimproved  forms  of  the  domestic  animals  are  too 
small  to  accomplish  successfully  the  work  required  by 
man.  This  demand  for  greater  size  and  generally  pro- 
portional increase  in  strength  has  led  breeders  consciously 
to  select  animals  for  size.  The  results  of  this  selection 
may  be  observed  in  the  gigantic  modern  draft  horse. 
It  is  probable  that  all  modern  breeds  of  horses  have 
developed  from  the  same  original  type.  The  wild  form 
was  small  in  size,  rough  and  somewhat  angular  in  appear- 
ance, with  short  mane  and  scanty  tail.  From  this  animal 
we  have  through  selection  succeeded  in  producing  the 
large,  powerful  draft  horse  with  smooth,  broad  contours 
and  heavy  mane  and  tail.  Contrasted  with  this  type 
we  have  well-recognized  pony  types  weighing  less  than 
400  pounds.  Both  types  undoubtedly  descend  from  the 

280 


THE   PRACTICE   OF  BREEDING  281 

same  prehistoric  form.  Each  type  breeds  true.  The 
chief  distinguishing  character  of  size  is  firmly  fixed  in  the 
germ-plasm  and  we  must  come  to  the  conclusion  that 
these  radical  differences  have  resulted  from  selection  and 
have  become  firmly  established  hereditary  characters. 
Similar  differences  in  size  among  cattle,  sheep  and  swine 
supply  additional  evidence  that  size  is  a  character  which 
may  be  radically  changed  through  selection  and  that  this 
variation  may  become  so  firmly  fixed  that  it  may  be  re- 
garded as  an  established  characteristic  of  the  breed. 

264.  Improvement  in  function.  —  The  most  remark- 
able achievements  in  the  improvement  of  the  domestic 
animals  are  undoubtedly  improvements  in  the  various 
physiological  functions  of  the  animals  useful  to  man. 
Some  of  the  most  noteworthy  of  these  are  the  milking 
function  in  cattle,  wool  production  in  sheep,  tendency 
to  fatten  in  meat  animals,  speed  in  horses  and  egg-laying 
in  the  domestic  fowls.     A  comparison  of  the  productivity 
of  each  of  these  types  of  animals  with  the  unimproved 
types  gives  ample  evidence  of  the  remarkable  develop- 
ment which  has  taken  place  through  the  agency  of  man's 
selection. 

265.  The   milking   function.  —  The   ability   of  mam- 
malian animals  to  produce  milk  is  closely  correlated  with 
the  reproductive  functions.    The  mammary  glands  func- 
tion primarily  for  the  purpose  of  supplying  a  nutritious 
and  easily  digested  food  for  very  young  animals.    Among 
wild, forms  this  function  persists  only  for  a  comparatively 
brief  period  and  its  continuance  is  determined  by  the 
needs  of  the  young  mammal.     Under  domestication  the 
milking  function  in  the  domestic  cow  represents  a  re- 
markable improvement.     The  wild  cow  probably  sup- 
plied milk  to  her  offspring  only  four  or  five  months.     The 


282  THE   BREEDING   OF  ANIMALS 

amount  of  milk  supplied  by  the  wild  cow  is  limited  to  a 
few  pounds  daily. 

The  milking  function  in  the  domestic  cow  has  become 
through  man's  selection  an  hereditary  character  of  the 
greatest  importance.  While  in  the  domestic  cow  the 
milking  function  is  still  closely  correlated  with  the  repro- 
ductive functions,  it  is  nevertheless  developed  to  such 
an  extent  that  it  bears  no  very  important  relation  to  the 
needs  of  the  young  offspring.  Certain  individual  cows 
have  this  function  developed  to  such  an  extraordinary 
degree  that  they  produce  milk  continuously  without  inter- 
ruption for  many  years  and  often  regardless  of  whether  the 
cow  becomes  pregnant  or  not.  (Plate  XXVI.) 

The  Holstein  Friesian  cow,  Duchess  Skylark  Ormsby 
(Plate  XXVII),  produced  27,761  pounds  of  milk  in  one 
year,  containing  1205  pounds  of  fat.  The  Jersey  cow, 
Sophie  19th  of  Hood  Farm  (Plate  XXVIII),  has  a  record 
of  17,557  pounds  of  milk  containing  999  pounds  of  fat. 
The  Guernsey  cow,  Murne  Cowan,  is  officially  reported  as 
having  produced  24,008  pounds  of  milk  and  1098  pounds 
of  butter-fat  in  one  year.  Garclaugh  May  Mischief,  an 
Ayrshire  cow,  has  a  similar  yearly  record  of  25,329 
pounds  of  milk  and  894  pounds  of  fat. 

266.  Improvement  in  wool  production.  —  The  first 
importations  of  Spanish  Merino  sheep  into  the  United 
States  were  made  about  1815.  At  that  time  the  average 
weight  of  fleece  was  three  or  four  pounds.  The  weight 
of  fleeces  of  American  Merinos  increased  gradually  from 
that  time  until  1885.  Authentic  records  of  single  fleeces 
weighing  from  thirty  to  forty  pounds  are  now  available. 
The  Oklahoma  Agricultural  College  has  reported  that 
the  two-year-old  Rambouillet  ram  Loraine  owned  by 
that  institution  has  produced  a  fleece  weighing  46  pounds 


THE   PRACTICE   OF   BREEDING  283 

which  is  claimed  to  be  the  heaviest  fleece  ever  taken  from 
a  single  sheep.  The  staple  of  this  fleece  was  three  and 
one-fourth  inches  in  length,  which  when  straightened 
measured  five  inches.  It  is  interesting  to  note  in  this 
case  that  the  fiber  was  of  unusual  fineness,  averaging 
YsTTo  °f  an  mcn  m  diameter.  According  to  Hunt,1  the 
average  weight  of  fleece  of  all  sheep  in  the  United  States 
in  1850  was  2.4  pounds  a  head.  In  1900  the  average 
weight  of  fleece  was  6.9  pounds  a  head.  This  remarkable 
development  in  the  improvement  of  the  wool-producing 
qualities  of  animals  must  be  wholly  credited  to  the  skill 
and  enterprise  of  the  American  shepherd. 

267.  Improvement  in  tendency  to  lay  on  fat.  —  It  is 
more  difficult  to  give  accurate  statistics  showing  the 
improvement  in  meat-producing  animals.  At  the  begin- 
ning of  the  eighteenth  century,  fat  animals  were  not 
placed  on  the  market  until  they  were  four  or  five  years  of 
age.  Even  as  late  as  1875,  three-  and  four-year-old  fat 
animals  were  the  most  common  types  of  cattle  to  be  found 
in  the  fat  stock  markets  of  America.  By  careful  selec- 
tion the  tendency  to  lay  on  fat  has  been  developed  in 
animals  to  such  an  extent  that  now  it  is  common  to  find 
young  animals  carrying  fat  equal  to  that  shown  by  four- 
and  five-year-old  bullocks  of  earlier  years.  This  tend- 
ency to  lay  on  fat  at  an  early  age  is  transmitted  through 
heredity.  The  amount  of  food  required  to  make  one 
pound  of  gain  is  much  less  in  the  younger  animals  and 
the  improvement  in  this  respect,  therefore,  is  of  great 
economic  significance.  It  requires  less  food  to-day  to 
produce  the  fat  beef,  pork  and  mutton  sold  in  the  markets 
of  the  World  than  was  the  case  before  the  improvement 
of  this  tendency  to  early  maturity.  (Plates  XXXI  and 
XXXII.) 

1  Hunt,  "  Cyclopedia  of  American  Agriculture,"  vol.  3. 


284  THE  BREEDING  OF  ANIMALS 

268.  Improvement  in  speed.  —  The  ability  to  go  fast 
at  the  trot  is  a  development  of  American  horse-breeding 
enterprise.     The  first  trotting  race  was  held  at  Boston 
in  1815.     The  fastest  time  made  in  this  race  was  a  mile 
in  three  minutes.     As  the  result  of  interest  in  trotting 
races  and  the  invention  of  light  horse-drawn  vehicles, 
the  demand  for  speed  at  the  trot  resulted  in  great  improve- 
ment in  this  direction.     The  record  time  of  trotting  horses 
decreased  from  year  to  year  until  at  the  present  day  (1916) 
several  horses  have  been  developed  that  are  able  to  trot 
a  mile  in  less  than  two  minutes.     The  examples  men- 
tioned are  all  noteworthy  as  examples  of  man's  power  to 
change   fundamentally   the   form   and   function   of   the 
domestic  animal.     These  examples  could  be  indefinitely 
multiplied. 

269.  Selection.  —  All  wild  forms  that  have  been  do- 
mesticated possess  characters  of  economic  value  to  man. 
They  were  domesticated  for  that  reason.     These  valuable 
qualities   have  been,  in  many  cases,  greatly   improved 
through  the  agency  of  man.     So  great  has  been  the  im- 
provement in  many  animal  forms  that  the  domesticated 
animal  is  markedly  different  from  his  wild  ancestors. 
Many  varieties,  races  or  breeds  exist  and  each  of  these 
differs  in  important  particulars  not  only  from  its  wild 
relatives  but  from  all  other  varieties  having  similar  ances- 
tral history. 

How  have  these  valuable  characteristics  come  into 
existence?  What  natural  laws  have  guided  man  in  the 
improvement  of  animals?  Are  the  valuable  character- 
istics of  animals  due  chiefly  to  inheritance  or  are  they  in 
most  part  the  result  of  improved  conditions  which  sur- 
round the  domestic  animals?  Is  it  possible  for  us  from 
a  study  of  the  history  of  the  achievements  of  animal- 


THE   PRACTICE   OF  BREEDING  285 

breeders  to  establish  a  guide  to  future  practice  in  the 
improvement  of  animals?  Answers  to  these  questions 
not  only  have  great  value  to  practical  breeders  but  have 
profound  biological  significance. 

270.  Natural  selection.  —  The  theory  of  natural  selec- 
tion which  has  so  long  influenced  and  determined  the 
trend  of  zoological  thought  is  an  attempt  to  explain  how 
the  qualities  of  animals  in  nature  have  come  to  be. 
Through  natural  selection  organic  beings  tend  to  adapt 
themselves  to  their  surroundings.  The  more  nearly 
the  qualities  of  animals  are  favorable  to  a  successful 
existence  under  the  cqnditions  surrounding  the  individual, 
the  more  certainly  will  the  animal  live  and  reproduce. 

The  insect  that  rests  upon  the  branches  of  trees  will 
escape  insectivorous  birds  more  certainly  if  the  color  of 
the  body  imitates  that  of  the  bark  upon  which  it  rests. 
The  color  of  the  jungle  animal  blends  so  completely  into 
the  general  landscape  that  its  presence  is  not  detected 
by  its  enemies. 

The  shore  birds  or  waders  in  their  pursuit  of  food  in  the 
shallow  waters  of  the  shore  have  developed  long  legs.  The 
giraffe,  feeding  as  it  does  upon  the  leaves  on  the  branches 
of  trees,  has  found  a  long  neck  to  be  a  desirable  quality  in 
securing  food.  And  in  this  case  the  longer  the  neck  the 
more  certainly  will  the  animal  survive  when  food  is  scarce. 

Darwin  assumed  that  under  conditions  similar  to  those 
mentioned,  animals  that  vary  slightly  in  the  desired 
direction  would  be  preserved  and  would  reproduce,  while 
those  animals  that  varied  away  from  the  valuable  quality 
would  perish.  An  animal  might  continue  to  develop 
indefinitely  in  a  given  direction  through  continuous 
variation.  Darwin  also  recognized  the  existence  of 
discontinuous  variation. 


286  THE  BREEDING   OF   ANIMALS 

The  origin  of  the  peculiar  characters  which  are  valuable 
in  the  domesticated  animal  is  believed  to  have  come 
about  through  a  similar  process  of  selection  but  with  this 
difference :  Man  has  introduced  methodical  selection  by 
which  all  animals  are  preserved,  not  only  those  suited 
to  their  particular  environment  but  also  and  chiefly  those 
which  possess  characteristics  that  are  valuable  to  man. 
Many  complex  and  difficult  questions  have  arisen  in  con- 
nection with  the  improvement  of  the  domesticated  ani- 
mals involving  the  most  difficult  problems  of  inheritance. 

271.  Methodical  selection.  —  The  selection  practiced 
by  man  is  known  as  methodical  selection.     Animals  are 
selected  because  of  their  peculiar  fitness  for  special  pur- 
poses.    The  powerful,  heavy  draft-horse  is  the  result  of 
generations  of  careful  selection  and  breeding  in  an  effort 
to  produce  an  animal  that  can  pull  heavy  loads. 

In  the  same  way  but  with  a  different  standard  of  selec- 
tion, the  speed  horse  has  developed  an  extraordinary 
ability  to  run  fast  under  the  saddle  or  trot  at  a  rapid  pace 
before  the  carriage. 

Similarly,  the  beef  animal,  the  dairy  cow,  the  mutton 
and  wool  sheep,  the  lard  and  bacon  hog,  the  swift  grey- 
hound, the  massive  St.  Bernard,  the  intelligent  Scotch 
collie  and  many  other  types  useful  to  man  have  come 
from  methodical  selection. 

272.  Importance   of  selection  in  animal-breeding.  — 
Careful  study  of  the  methods  which  have  been  practiced 
by  breeders  of  the  domestic  animals  cannot  fail  to  lead 
to  the  inevitable  conclusion  that  selection  has  been  the 
most  important  if  not  the  chief  principle  followed  in  bring- 
ing about  the  present  highly  developed  forms  among 
animals. 

Certainly  not  all  the  phenomena  which  are  exhibited 


PLATE  XXIX.  —  Daughters  of  the  same  sire,  illustrating  great  uniformity 
in  conformation  and  productive  power  resulting  from  the  use  of  a  prepotent 
sire  in  the  herd.  These  three  cows  have  an  average  yearly  record  of  22,295 
pounds  of  milk  and  855  pounds  of  butter.  Owner,  University  of  Missouri. 


PLATE  XXX.  —  Three  generations  showing  impressive  character  of 
original  dam.  Upper,  Missouri  Chief  Josephine,  yearly  milk  record  26,861 
pounds.  Middle,  Missouri  Josephine  Sarcastic,  daughter,  yearly  milk  record 
18,452  pounds.  Lower,  Carlotta  Campus  Girl,  granddaughter,  yearly  milk 
record  15,725  pounds  as  a  two-year-old.  Owner,  University  of  Missouri. 


THE   PRACTICE   OF   BREEDING  287 

in  the  practices  and  results  of  animal-breeders  can  be 
explained  upon  the  basis  of  selection  alone,  but  it  is  quite 
certain  that  without  selection  little  practical  use  could 
be  made  of  the  known  laws  which  govern  the  transmission 
of  characters.  Man's  chief  agency  in  the  improvement 
of  animals  has  not  been  a  conscious  effort  to  bring  about 
a  series  of  variations  or  mutations  of  a  certain  kind,  but 
it  has  rather  been  in  the  direction  of  preserving  such 
valuable  characteristics  as  have  been  already  in  existence 
or  have  appeared  through  variation.  These  character- 
istics have  been  intensified  by  judicious  matings  and 
perpetuated  as  a  result  of  the  keen  insight  of  the  skillful 
breeder.  The  successful  breeder  has  ever  in  mind  an 
ideal.  He  is  at  all  times  alert  to  detect  variations  which 
approach  this  ideal. 

Darwin  believed  that  most  of  the  improvement  wrought 
in  domestic  animals  was  due  to  minute  or  continuous 
variations  from  the  less  desirable  to  the  more  desirable. 
This  belief  has  been  general  among  animal-breeders 
themselves.  Working  upon  this  assumption,  the  work  of 
the  breeder  consisted  merely  in  accurately  observing  the 
variations  which  tended  in  the  desired  direction. 

But  continuous  variation  assumes  a  perfect  series  of 
infinitesimal  steps,  each  grading  into  the  one  higher  or 
lower.  Such  continuity  exists  in  the  growth  of  animals 
from  birth  to  maximum  development.  Continuous  varia- 
tion is  also  illustrated  in  the  physical  world  by  changes 
in  temperature.  In  the  history  of  the  improvement  of 
domestic  animals  there  are  many  examples  of  marked 
and  sudden  variations  in  the  offspring  which  cannot 
be  continuous.  Such  variations  have  been  called  dis- 
continuous variations  or  mutations.  It  is  certain  that 
much  of  the  improvement  in  the  domestic  animals  has 


288  THE  BREEDING  OF  ANIMALS 

come  from  valuable  mutations  which  have  been  recognized 
by  the  alert  breeder. 

But  whether  the  present  valuable  characteristics  of 
the  domestic  animals  have  come  through  continuous 
variations  or  by  sudden  mutations  or  in  any  other  way, 
selection  by  man  has  been  the  one  outstanding  fact  in 
the  development  of  the  many  valuable  races  and  breeds 
of  animals.  It  is  conceivable  and  very  probable  that 
similar  variations  have  been  induced  by  similar  causes 
in  all  wild  forms,  but  wild  forms  have  remained  relatively 
stationery  while  the  domestic  races  have  been  greatly 
improved. 

273.  Aids  to  selection.  —  The  breeder  has  consciously 
or  unconsciously  brought  to  his  aid  numerous  practices 
which  have  greatly  facilitated  his  efforts.  The  manu- 
facturer who  has  invented  a  labor-saving  device  or  a 
complicated  machine  to  perform  certain  work  puts  it  to 
the  test  by  actually  applying  the  machine  to  the  work 
in  hand.  Likewise  the  skillful  breeder  has  found  it  greatly 
to  his  advantage  to  test  his  animal  creations  by  actual 
performances. 

The  breeders  of  trotting  horses  have  no  means  of  deter- 
mining how  successful  they  are  in  producing  speed  except 
by  trial  on  the  track  and  it  is  not  only  necessary  to  train 
now  and  then  a  horse  but  every  individual  in  the  stud 
must  be  tested  to  be  certain  that  all  possess  the  quality 
of  speed. 

The  highly  successful  breeders  of  meat  animals,  cattle, 
sheep  and  swine,  maintain  their  breeding  animals  in  a 
high  state  of  condition.  In  some  cases  the  meat  animals 
used  for  breeding  purposes  by  noted  breeders  are  kept 
so  fat  as  to  interfere  with  the  normal  reproductive  func- 
tions. But  even  so,  such  a  practice  is  essential  to  the 


THE   PRACTICE   OF   BREEDING  289 

skillful  breeder  because  in  no  other  way  can  he  determine 
whether  or  not  his  breeding  animals  themselves  possess 
the  proper  tendency  to  lay  on  fat  which  is  an  essential 
characteristic  of  a  well-improved  meat  animal. 

A  high  condition  of  the  breeding  animals  does  not 
in  any  sense  give  the  beef  animal  a  greater  power  to  trans- 
mit the  tendency  to  lay  on  fat  to  the  offspring,  as  some 
breeders  have  believed,  but  it  does  give  him  a  selective 
device  or  measure  by  which  he  may  always  know  whether 
his  breeding  animals  themselves  possess  the  characters 
which  it  is  desired  to  transmit  to  the  offspring. 

The  breeders  of  dairy  cattle  feed  their  cows  to  full 
capacity  and  surround  them  with  every  favorable  condi- 
tion for  the  maximum  production  of  milk.  This  practice 
gives  the  breeder  the  only  accurate  measure  of  individual 
performance  and  places  in  his  hand  a  selective  device  by 
means  of  which  he  can  quickly  eliminate  from  his  herd 
those  animals  that  have  not  inherited  the  capacity  for 
high  production.  There  is  no  other  accurate  measure- 
ment which  the  breeder  can  employ  that  will  certainly 
register  his  progress  in  the  improvement  of  his  favorite 
breed. 

274.  Theo-eal  results  of  selection  in  the  improvement 
of  the  domestic  animals.  —  The  many  improved  breeds 
of  live-stock  which  are  now  possessed  of  qualities  of  great 
economic  value  to  man,  have  come  to  this  possession 
through  artificial  selection  practiced  by  man.  Are  these 
qualities  which  distinguish  the  improved  breed  from  the 
wild  form  a  permanent  possession  of  the  race?  Have 
the  selective  processes  applied  by  man  resulted  in  so  fixing 
the  desirable  heritable  characteristics  that  the  breeder 
may  depend  upon  inheritance  to  repeat  the  characters 
of  the  parents  in  the  offspring?  There  are  some  indi- 


290  THE   BREEDING   OF   ANIMALS 

viduals  in  each  breed  that  represent  near  perfection  in 
the  development  of  characters.  There  are  many  others 
that  are  more  or  less  deficient  in  such  characters  while 
other  individuals  are  actually  mediocre.  Will  the  indi- 
vidual with  near  perfect  characters  reproduce  other 
individuals  of  the  same  high  quality  ?  Will  the  mediocre 
sort  beget  like  mediocrity  ?  In  other  words,  are  the  quali- 
ties which  have  resulted  from  artificial  selection  indelibly 
impressed  on  the  hereditary  substance  of  the  germ-plasm 
in  such  a  way  as  to  be  certainly  transmitted  to  the  off- 
spring? Exact  answers  to  these  questions  cannot  be 
given  without  full  knowledge  of  all  the  conditions,  but 
recent  investigations  have  thrown  much  light  on  these 
important  questions. 

275.  Selection  within  pure  lines.  —  Selection  as  prac- 
ticed by  man  has  undoubtedly  resulted  in  marked  im- 
provement of  the  domestic  animals.  This  improvement 
is  apparently  transmitted,  or  at  least  it  is  possible  by 
continued  selection  to  reproduce  desirable  characteristics. 
By  continually  selecting  individual  breeding  animals 
which  show  a  tendency  to  vary  in  the  direction  desired, 
it  has  been  assumeol.  that  the  race  or  breed  would  gradu- 
ally move  in  the  direction  of  selection.  ^ 

At  one  period  in  the  history  of  Shorthorn  cattle,  all 
breeders  were  agreed  that  their  improvement  was  mainly 
to  be  accomplished  in  the  direction  of  increased  size. 
Consequently  the  animals  of  greatest  scale  were  selected 
and  mated  with  the  apparent  result  that  the  average  size 
of  the  breed  was  increased.  But  actually  what  was 
accomplished  after  many  generations  of  selection?  Was 
a  new  breed  created?  Had  selection  acted  as  a  causa- 
tive principle?  The  teachings  of  Darwin  and  his  fol- 
lowers has  undoubtedly  resulted  in  creating  the  impres- 


THE   PRACTICE   OF   BREEDING  291 

sion  among  many  students  that  in  this  case  a  new  breed 
had  actually  been  created  with  new  characters  resulting 
from  selection  of  continuous  variations.  That  the  results 
obtained  in  this  and  similar  examples  may  te  explained 
on  other  and  more  probable  grounds  has  been  clearly 
demonstrated  by  Johannsen.1  This  Danish  botanist 
working  with  garden  beans  found  that  the  whole  popula- 
tion is  made  up  of  many  races  which  he  called  "  pure 
lines."  Selecting  from  populations  composed  of  pure 
lines,  the  breeder  merely  sorts  out  one  of  these  races 
and  in  time  secures  a  pure  line.  This  pure  line  or  race 
is  not  new.  It  has  not  resulted  from  gradual  or  continu- 
ous variations  but  has  simply  been  separated  out  from 
a  number  of  others.  According  to  Johannsen,  selec- 
tion within  a  pure  line  during  a  number  of  generations 
had  no  effect  in  improving  the  variety.  The  germ- 
plasm  of  all  individuals  of  a  pure  line  tends  to  become 
homogeneous. 

The  mating  of  individuals  from  a  pure  line  having 
in  their  respective  germ-plasms  identical  factors  will 
result  in  producing  identical  offspring  and  hence  any 
amount  of  selection  will  prove  futile.  Such  pure  line 
individuals  are  much  more  likely  to  be  found  among  plants 
than  among  animals.  Plants  that  are  self-fertilizing  may 
be  expected  to  develop  typical  pure  lines  and  selection 
within  such  pure  lines  will  be  of  no  avail.  Among  the 
higher  animals  similar  results  undoubtedly  occur,  but 
the  difficulties  of  securing  a  strictly  pure  line  are  very 
much  greater  owing  to  the  necessity  of  mating  two  dis- 
tinct individuals  whose  ancestry,  while  similar,  cannot 
possibly  from  the  very  nature  of  the  case,  be  exactly 
identical. 

1  Johannsen,  "Elemente  der  exakten  Erblichkeitslehre,"  1909. 


292  THE  BREEDING   OF   ANIMALS 

276.  Vilmorinvs  pure  line  wheat-breeding.  —  A  good 
example  of  the  pure  line  theory  among  plants  is  to  be 
found   in  the  very  practical   and  meritorious  work  of 
Louis  de  Vilmorin,  who  began  the  improvement  of  com- 
mercial varieties  of  wheat  in  France  about  1840.     Vil- 
morin carefully  selected  a  single  head  of  outstanding  merit 
and  from  this  by  in-breeding  established  a  pure  line  or 
variety  which  has  bred  true  to  the  original  ear  or  head. 
The  commercial  seed  offered  by  Vilmorin  was  always 
descended  from  a  single  plant.     Selection  in  this  case 
failed  to  bring  about  any  improvement  over  the  original 
plant,  as  shown  by  the  Hagadoorns.1 

"  In  1911  Mr.  Meunissier,  the  genetist  of  the  firm  of 
Vilmorin,  found  the  collection  of  original  ears  of  the  varie- 
ties with  which  Louis  de  Vilmorin  half  a  century  back 
began  his  living  museum.  Some  of  these  wheats  are 
from  the  harvest  of  1843,  others  date  from  1850,  or  inter- 
mediate dates.  Mr.  Meunissier  chose  three  dozen  ears 
of  varieties  which  are  still  in  the  collection,  and  which 
have  therefore  been  bred  continuously  as  pure  lines  for 
about  fifty  years.  We  compared  these  ears  to  ears  of 
the  1911  harvest,  and  photographed  them  side  by  side. 
Some  of  these  pairs xof  ears  are  here  shown,  each  pair  con- 
sisting of  the  old  ear,  and  its  descendant,  half  a  century 
later.  All  these  generations  of  selection  have  not  changed 
any  one  of  the  varieties  one  little  bit.  It  can  therefore 
safely  be  concluded  from  this  series  of  experiments,  that 
selection  can  have  no  effect,  in  material  pure  for  its 
genetic  factors.  Genetic  factors  are  constant." 

277.  Selection  most  useful  when  genetic  factors  are 
not  pure.  —  The  pure  line  theory   explains    why    any 

1  Mrs.  C.  and  Dr.  A.  L.  Hagadoorn,  "Selection  in  Pure  Lines," 
American  Breeder's  Magazine,  1913,  p.  165. 


THE   PRACTICE   OF   BREEDING  293 

improvement  among  the  best  strains  of  animals  is  so 
difficult.  Highly  improved  breeds  or  families  among 
the  domestic  animals  have  reached  a  degree  of  purity 
wherein  the  germ-plasm  represents  an  approach  to  homo- 
geneity. When  such  a  pure  line  has  been  established, 
the  old  adage  that  "  like  begets  like  "  becomes  a  really 
working  principle  and  a  guide  to  practice.  The  novice 
need  not  expect  to  accomplish  great  improvement  in  the 
highly  developed  breeds  of  live-stock.  The  greatest 
improvement  will  be  made  in  breeds  or  strains  of  mixed 
breeding,  genetically  speaking. 

The  improvement  of  animals  of  mixed  character  which 
will  result  from  the  efforts  of  a  breeder  is  probably  to  be 
explained  as  a  gradual  separation  of  the  desirable  pure 
lines  and  mating  the  individuals  which  possess  these 
characters.  This  results  in  time  in  the  establishment  of 
a  strain  or  breed  which  is  prepotent  in  transmitting  the 
desired  qualities  when  after  many  generations  of  pure 
line  breeding  this  strain  has  reached  a  point  where  the 
germ-plasm  of  the  breeding  animals  is  pure  in  respect 
to  its  genetic  factors ;  then  any  considerable  improvement 
will  be  no  longer  possible. 

278.  Pure  line  theory  not  opposed  to  improvement  by 
selection.  —  The  practical  breeder  whose  experience  has 
demonstrated  clearly  that  improvement  among  the  regis- 
tered or  "  pure-bred  "  races  of  the  domestic  animals  has 
followed  careful  and  persistent  selection  will  hesitate 
to  accept  the  statement  of  Johannsen  and  his  followers 
that  "  selection  within  the  pure  line  is  without  effect." 
But  the  improved  breeds  of  live-stock,  however  pure 
in  breeding,  are  not  to  be  regarded  as  fulfilling  the  require- 
ments of  a  "  pure  line  "  in  the  biological  sense.  The 
breeds  of  live-stock  are  yet  far  from  homogeneous  in 


294  THE  BREEDING  OF   ANIMALS 

the  sense  that  they  have  been  selected  to  a  point  where 
the  germ-plasm  of  different  individuals  of  the  breed,  is 
identical  in  composition.  The  pure  line  of  the  biologist 
is  after  all  a  purely  imaginary  conception.  It  is  conceiv- 
able that  such  a  condition  may  be  produced  among  self- 
fertilizing  plants,  but  among  the  higher  animals  it  is 
certainly  true  that  no  such  germinal  purity  has  yet  been 
attained.  The  practical  animal-breeder  may  still  con- 
tinue to  hold  fast  to  selection  as  his  chief  means  of  im- 
provement with  the  assurance  that  in  all  the  higher  do- 
mestic animals  we  have  not  yet  reached  the  ultimate 
limits  of  improvement.  The  animal-breeder  has  not 
yet  produced  a  pure  line,  biologically  speaking,  and  has 
not,  therefore,  reached  a  point  in  his  breeding  when  it 
can  be  accurately  said  that  selection  is  without  effect.1 

279.  Pedigree.  —  The  pedigree  of  an  animal  is  a  record 
of  the  ancestors.  It  is  a  valuable  historical  document. 
If  it  includes  the  names  of  many  animals  of  outstanding 
quality,  it  is  a  good  pedigree.  If  the  ancestors  were 
mediocre  individuals  of  no  special  merit,  the  pedigree 
is  inferior.  The  mere  fact  that  an  animal  is  recorded  in 
a  recognized  herd-book  does  not  signify  that  such  animal 
has  a  good  pedigree.  The  careful  breeder  must  have  a 
thorough  knowledge  of  the  history  of  the  breed  and  espe- 
cially of  the  ancestors  of  the  individual  animal  under 
examination. 

The  immediate  ancestors  are  most  important.  A 
noted  sire  or  dam  appearing  in  the  pedigree  six  or  eight 
generations  back  is  of  far  less  importance  than  one  which 
appears  in  the  first,  second  or  third  generations.  Many 
breeding  animals  are  sold  on  the  strength  of  the  fact 

Castle,  "Pure  Lines  and  Selection,"  Journal  of  Heredity, 
1914,  p.  93. 


THE   PRACTICE   OF   BREEDING  295 

that  they  are  descended  from  some  famous  sire  or  dam 
ten  or  even  twenty  generations  back.     If  Galton's  law 
of  ancestral  heredity  is  a  fair  estimate  of  the  potential 
strength  of  a  breeding  animal,  we  should  expect  that 
the  individual  animal  would  inherit  one-half  from  his 
two  immediate  parents,  one-fourth  from  his  four  grand- 
parents, and  one-eighth  from  his  eight  great-grandparents. 
From  one  great-grandparent,  therefore,  we  should  expect 
the  inheritance  in  the  descendant  to  be  represented  by 
the  fraction  -^.     It  is  evident  that  a  single  ancestor  six 
or  eight  generations  removed  would  contribute  a  very 
small  fraction  of  the  sum  total  of  qualities  of  the  individual. 
In  the  application  of  Galton's  principle,  it  is  necessary 
to  assume  that  all  the  ancestors  are  equally  prepotent. 
This  assumption  is  contrary  to  the  experience  of  breeders. 
Certain   individuals   are  known  to   be  more   prepotent 
in  certain  characters,  or,  more  properly  speaking,  certain 
characters    are    dominant    and    others    recessive.     The 
dominant  characters  will  largely  determine  the  character 
of  the  offspring.     It  is  conceivable  that  a  dominant  char- 
acter which  it  is  greatly  desired  to  perpetuate  in  a  strain 
might  reappear  in  the  offspring  through  many  genera- 
tions.    It  might  be  argued  that  because  of  this  fact  a 
study  of  the  characters  of  an  ancestor  far  removed  hav- 
ing this  character  would  be  valuable.    To  this  it  must 
be  said  that  if  the  character  is  dominant  it  will  be  clearly 
apparent  in  the  immediate  ancestors.     If  it  is  not  apparent 
it  may  have  been  lost  or  overshadowed  by  the  develop- 
ment of  other  characters,  and  if  so  it  is  good  evidence  that 
the  real  character  of  the  strain  is  being  determined  by 
nearer  and  stronger  ancestors.     Every  modern  biological 
conception  gives  added  weight  to  the  principle  that  it  is 
the  recent  ancestors  that  should  be  most  carefully  in- 


296  THE   BREEDING  OF  ANIMALS 

vestigated  by  the  practical  breeder  if  he  is  to  obtain  any 
valuable  basis  for  estimating  the  breeding  powers  of  an 
individual. 

280.  Registered  breeding  animals.  —  In  purchasing 
a  breeding  animal,  the  breeder  desires  some  guarantee 
of  purity  of  breeding.  Every  recognized  breed,  therefore, 
maintains  an  association  of  breeders  organized  for  the 
purpose  of  safeguarding  the  purity  of  the  breeding  ani- 
mals and  advancing  the  general  interests  of  the  breed. 
Each  association  maintains  a  record  book  in  which  every 
animal  recognized  as  a  pure-bred  animal  of  the  breed  is 
recorded.  Each  association  has  its  own  rules  governing 
the  registration  of  animals.  In  practically  all  breed 
associations,  the  offspring  of  registered  parents  can  be 
recorded.  There  are  few  exceptions  to  this  rule.  In 
some  associations  animals  may  be  registered  upon  the 
basis  of  their  performance.  The  Standard  Bred  or 
American  Trotting  Horse  Registry  Association  will  record 
any  animal  that  has  made  an  authentic  record  of  a 
mile  in  two  minutes  and  thirty  seconds  on  an  approved 
track  and  under  regulation  rules.  A  few  associations  in 
the  past  have  permitted  the  registration  of  animals  hav- 
ing a  certain  number  of  top  crosses  to  registered  sires. 
The  history  of  all  breed  associations  is  similar.  A  few 
animals  of  similar  characters  have  attracted  attention 
because  of  their  peculiar  value  for  certain  purposes. 
These  animals  have  been  interbred  and  gradually  a  family 
or  strain  developed  which  excels  in  certain  valuable 
characteristics.  The  admirers  of  this  family  or  strain 
have  organized  to  preserve  the  strain.  Experience  has 
shown  that  one  of  the  first  and  most  useful  steps  is  to 
record  the  individual  breeding  animals  of  outstanding 
merit.  The  descendants  of  these  animals  constitute 


THE   PRACTICE   OF   BREEDING  297 

the  breed,  and  ultimately  only  descendants  of  animals 
recorded  in  the  registry  book  are  eligible  to  registration. 
281.  Registry  associations.  —  The  recognized  registry 
associations  of  the  United  States  at  present  (1916)  are 
listed  below : 1 

AMERICAN    HORSE    RECORD    ASSOCIATIONS 

Arabian  Horse  Club  of  America. 

American  Association  of  Importers  and  Breeders  of  Belgian 

Draft  Horses. 

Cleveland  Bay  Society  of  America. 
American  Clydesdale  Association. 
French  Coach  Horse  Society  of  America. 
National  French  Draft  Horse  Association  of  America. 
German,  Hanoverian  and  Oldenburg  Coach  Horse  Association 

of  America. 

American  Hackney  Horse  Society. 
American  Morgan  Register  Association. 
Percheron  Society  of  America. 

The  American  Breeders'   and   Importers'   Percheron   Registry 
*        Company. 

American  Saddle  Horse  Breeders'  Association. 
American  Shetland  Pony  Club. 
American  Shire  Horse  Association. 
American  Suffolk  Horse  Association. 
American  Trotting  Register  Association. 
The  Jockey  Club. 
The  Welsh  Pony  and  Cob  Society  of  America. 

AMERICAN  JACKS  AND   JENNET   RECORD 
ASSOCIATIONS 

American  Breeders'  Association  of  Jacks  and  Jennets. 
Standard  Jack  and  Jennet  Registry  of  America. 

AMERICAN  CATTLE  RECORD  ASSOCIATIONS 

American  Aberdeen-Angus  Breeders'  Association. 

Ayrshire  Breeders'  Association. 

Brown  Swiss  Cattle  Breeders'  Association. 

1  Data  from  United. States  Department  of  Agriculture. 


298  THE  BREEDING   OF   ANIMALS 

American  Devon  Cattle  Club. 

Dutch  Belted  Cattle  Association  of  America. 

American  Galloway  Breeders'  Association. 

American  Guernsey  Cattle  Club. 

American  Hereford  Cattle  Breeders'  Association. 

Holstein-Friesian  Association  of  America. 

American  Jersey  Cattle  Club. 

American  Kerry  and  Dexter  Cattle  Club. 

Polled  Durham  Breeders'  Association. 

American  Polled  Hereford  Breeders'  Association. 

Red  Polled  Cattle  Club  of  America,  Inc. 

American  Shorthorn  Breeders'  Association. 

American  Dairy  Shorthorn  Cattle  Club. 


AMERICAN   SHEEP   RECORD   ASSOCIATIONS 

American  Cheviot  Sheep  Society. 

American  Cotswold  Registry  Association. 

The  Continental  Dorset  Club. 

American  Hampshire  Sheep  Association. 

American  Leicester  Breeders'  Association. 

National  Lincoln  Sheep  Breeders'  Association. 

American  and  Delaine  Merino  Record  Association. 

Dickinson  Merino  Sheep  Record  Company. 

National  Delaine  Merino  Sheep  Breeders'  Association  of  Wash- 
ington County. 

Standard  Delaine  Merino  Sheep  Breeders'  Association. 

American  Rambouillet  Sheep  Breeders'  Association. 

International  Von  Hom,eyer  Rambouillet  Club. 

Michigan  Merino  Sheep  Breeders'  Association. 

Vermont,  New  York,  and  Ohio  Merino  Sheep  Breeders'  Asso- 
ciation. 

American  Oxford  Down  Record  Association. 

American  Romney  Marsh  Breeders'  Association. 

American  Shropshire  Registry  Association. 

American  Southdown  Breeders'  Association. 

American  Tunis  Sheep  Breeders'  Association. 


GOATS 

American  Angora  Goat  Breeders'  Association. 
American  Milch  Goat  Record  Association. 


THE   PRACTICE   OF   BREEDING  299 

AMERICAN    SWINE    RECORD    ASSOCIATIONS 

American  Berkshire  Association. 

American  Large  Black  Pig  Society. 

Cheshire  Swine  Breeders'  Association. 

O.  I.  C.  Swine  Breeders'  Association. 

Chester  White  Record  Association. 

American  Duroc  Jersey  Swine  Breeders'  Association. 

National  Duroc  Jersey  Record  Association. 

American  Hampshire  Swine  Record  Association. 

American  Poland  China  Record  Company. 

National  Poland  China  Record  Company. 

Standard  Poland  China  Record  Association. 

American  Tamworth  Swine  Record  Association. 

American  Yorkshire  Club. 

National  Mule-foot  Hog  Association. 

Mule-foot  Hog  Breeders'  Association. 

American  Mule-foot  Hog  Record  Company. 

282.  Community  breeding.  —  The  establishment  and 
maintenance  of  a  recognized  breed  is  a  cooperative  enter- 
prise. No  single  individual  can  alone  successfully  estab- 
lish and  maintain  a  breed.  Other  things  being  equal, 
the  larger  the  number  of  breeders  engaged  in  the  improve- 
ment of  a  given  breed,  the  more  certainly  will  the  breed 
be  improved  and  established  on  a  permanent  foundation. 
It  is  also  true  that  it  is  distinctly  to  the  advantage  of  a 
breed  to  be  owned  by  breeders  living  in  the  same  region. 
The  interests  of  the  breeders  are  greatly  enhanced  if 
many  workers  in  a  restricted  area  are  breeding  the  same 
class  of  animals.  This  is  particularly  true  in  the  case  of 
the  person  who  maintains  a  small  herd  or  flock.  The 
economic  value  of  establishing  for  a  community  the  repu- 
tation of  breeding  a  very  large  number  of  a  certain  breed 
has  been  demonstrated  in  many  localities  in  this  and 
other  countries.  Recognizing  these  advantages,  educa- 
tional organizations  and  breed  associations  have  encour- 
aged community  breeding  enterprises.  In  some  localities 


300  THE  BREEDING  OF  ANIMALS 

this  has  taken  the  form  of  cooperation  among  three  or 
four  small  breeders  in  the  purchase  of  a  valuable  bull. 
In  the  United  States  many  associations  have  been  formed 
among  farmers  for  the  purchase  of  a  valuable  stallion. 
Even  in  the  absence  of  conscious  cooperation  for  improve- 
ment, if  a  large  number  of  the  farmers  in  a  given  neigh- 
borhood are  like-minded  in  the  selection  of  breeds  and 
all  produce  the  same  breeds,  each  particular  animal  will 
actually  be  more  valuable  because  prospective  buyers 
will  be  attracted  by  the  opportunity  for  selection  where 
large  numbers  are  available. 

283.  Importance    of    numbers.  —  The    present    high 
quality  of  the  highly  improved  and  valuable  breeds  of  the 
domestic  animals  has  been  the  result  of  long-continued 
and  rigid  selection.     The  perpetuation  of  the  improved 
characters  already  obtained  rests  upon  the  opportunity 
for  continued  selection  of  the  same  kind.     The  effective- 
ness of  selection  will  depend  upon  the  number  of  individual 
animals  which  are  concerned  in  any  given  breeding  proj- 
ect.    It  follows,  therefore,  that  the  breeder  who  produces 
large  numbers  has  a  decided  advantage  over  the  one 
whose  opportunity  for  selection  has  been  confined  to  a 
relatively  small  nuniber  of  animals.     A  noted  breeder  of 
dogs  who  was  asked  to  give  the  secret  of  his  success  replied, 
"  I  breed  many  and  hang  many."    The  breeder  whose 
operations  are  limited  to  a  relatively  small  flock  or  herd 
cannot  expect  to  accomplish  as  much  in  the  improvement 
of  any  class  of  animals  as  the  breeder  handling  much 
larger  numbers. 

284.  Selecting  the  best.  —  The  improvement  of  ani- 
mals has  come  chiefly  through  selection.     In  the  actual 
process  of  selection,  men  have  followed  various  methods 
with  the  ultimate  purpose  of  obtaining  finally  a  race  or 


THE   PRACTICE  OF 'BREEDING  301 

breed  of  fixed  characters,  that  is,  characters  which  are 
represented  by  definite  determiners  in  the  germ-plasm 
in  such  a  way  that  the  individual  animals  of  the  breed 
are  able  to  transmit  these  desirable  characters  to  their 
offspring  with  a  reasonable  degree  of  certainty.  Thus 
many  breeders  have  surrounded  their  animals  or  plants 
with  exceptionally  favorable  conditions  and  have  selected 
those  which  have  developed  the  prized  qualities  most 
perfectly  under  such  conditions.  This  was  the  method 
of  Hallet  in  developing  improved  varieties  of  wheat.  Un- 
doubtedly many  of  the  early  breeders  based  this  practice 
upon  a  very  deep-seated  but  mistaken  belief  in  the  in- 
heritance of  acquired  characters.  This  method  has  been 
very  successful  in  a  considerable  number  of  cases,  both 
among  plants  and  animals,  but  not  because  the  environ- 
mental factors  involved  had  fundamentally  changed  the 
real  character  of  the  germ  substance.  In  all  such  cases 
the  improved  environment  acted  merely  as  an  efficient 
selective  device  and  indicated  those  individuals  which 
actually  possessed  the  capacities  valued  by  the  breeder. 
This  method  has  often  failed  in  accomplishing  lasting 
improvement,  because  the  conditions  surrounding  the 
breeding  stock  are  not  average  conditions  and  the  appar- 
ent improvement  may  be  wholly  due  to  a  better  food 
supply  or  more  room  and  not  due  to  fundamental  differ- 
ences in  the  germ.  Another  method  of  improvement 
which  involves  selection  of  the  best  is  to  place  the  plant 
or  animal  under  ordinary  or  even  unfavorable  conditions 
and  select  those  individuals  which  appear  best  able  to 
develop  the  desired  qualities  under  such  conditions. 

285.  Selecting  chance  variations.  —  We  know  that 
sudden  and  important  variations  often  occur  in  the  germ- 
plasm.  Some  of  these  variations  may  be  of  such  a  char- 


302  THE  BREEDING   OF  ANIMALS 

acter  as  to  have  great  economic  value  to  man.  Varia- 
tions of  this  character  are  invariably  transmitted,  and  the 
wise  and  observant  breeder  may  often  make  rapid  prog- 
ress by  making  such  chance  variation  the  basis  of  his 
selections.  This  is  the  method  of  De  Vries.  In  following 
this  method  the  breeder  does  not  consciously  undertake 
to  cause  variation  but  rather  to  take  advantage  of  those 
which  have  resulted  from  natural  causes.  The  breeder 
of  the  domestic  animals  will  often  have  difficulty  in  deter- 
mining whether  a  given  variation  is  due  to  environmental 
causes  or  is  due  to  fundamental  changes  in  the  germ-plasm. 
The  skillful  breeder,  however,  will  conclude  with  reason- 
able assurance  that  when  an  individual  animal  exhibits 
a  rare  and  unusual  aptitude  in  the  development  of  a 
certain  character  or  characters,  in  a  herd  in  which  the 
individuals  are  all  maintained  under  identical  conditions, 
the  rare  development  may  be  regarded  as  a  germinal 
variation.  Such  germinal  variations  may  under  certain 
conditions  become  the  foundation  of  a  new  strain. 

286.  The  Burbank  method.  —  If  the  selection  of  varia- 
tions is  the  road  to  success  in  improvement,  then  why  not 
systematically  attempt  to  cause  variations  and  thus 
increase  the  chances  for  discovering  a  desirable  mutation  ? 
This  is  the  plan  followed  by  Burbank.  By  crossing  a 
great  number  of  individuals,  variations  are  secured,  and 
by  a  process  of  gradual  elimination  the  outstanding  vari- 
ants are  retained  and  reproduced.  This  plan  does  not 
create  any  new  forms,  but  depends  on  the  well-known 
tendency  of  unit  characters  to  rearrange  themselves  in 
new  combinations  which  for  all  practical  purposes  may 
really  become  a  new  creation.  This  method  involves 
the  propagation  of  the  improved  individual  by  budding, 
grafting  or  similar  asexual  method  and  cannot  therefore 


THE   PRACTICE  OF  BREEDING  303 

be  successfully  applied  in  animal-breeding.  This  method, 
like  all  the  others  described,  is  open  to  the  objection  that 
it  is  after  all  based  on  mere  chance.  It  is  empirical  and 
unscientific.  The  proportion  of  failures  to  successes  is 
too  great,  and  for  these  reasons  it  is  a  slow  process  of  im- 
provement. 

287.  The  mendelian  method.  —  The  mendelian  method 
is  based  on  the  law  of  dominance  and  the  segregation  of 
unit  characters.  The  first  step  is  to  determine  by  the 
behavior  of  the  desired  character  in  transmission  whether 
it  is  a  dominant  or  a  recessive  character.  If  it  is  recessive, 
then  it  is  only  necessary  to  combine  two  recessives,  as 
recessives  are  homozygous  and  always  breed  true.  If 
the  desired  character  proves  to  be  a  dominant,  it  is  first 
necessary  to  determine  whether  it  is  present  in  a  heterozy- 
gous or  a  homozygous  condition.  If  it  is  homozygous,  it 
will  breed  true.  If  it  is  heterozygous,  by  in-breeding  and 
gradually  eliminating  the  recessives  it  is  possible  greatly 
to  increase  the  number  of  dominants  appearing  and  thus 
practically  establish  a  pure  strain.  This  method  is  also 
more  successful  in  plant-  than  animal-breeding.  The 
animal  characters  which  have  come  to  be  recognized  as  of 
value  to  man  are  generally  complex  and  do  not  behave 
in  transmission  as  unit  characters. 


INDEX 


Abortion,  120. 

a  cause  of  sterility,  120. 

agglutination  test  for,  128. 

contagious,  123. 

diagnosis  of,  127. 

treatment  of,  124. 
Acquired  characters,  157-160,  162. 

examples  of,  162. 

influenced  by  food  supply,  162. 
Acquired  diseases,  180. 
Age  and  fecundity,  96. 

of  poultry  affects  fertility,  96. 

of  ram  influences  fertility,  94. 

of  sheep  influences  fertility,  93. 

of  swine  influences  fertility,  91. 
Age  factor  in  animal-breeding,  271. 
Agglutination   test   for   contagious 

abortion,  128. 

Anaphase  in  cell  division,  12. 
Arkell,  187. 

Artificial  insemination  methods,  44. 
Asexual  reproduction,  16. 
Ash  in  ration,  effect  on  foetus,  263. 
Atwood,  94. 

Bachhuber,  50. 

Barrenness,  see  also  sterility,  119. 
Bateson,  210. 
Beard,  76. 

Beinn  Bhreagh  flock,  fertility  of,  99. 
Bell,  99. 
Berberrich,  89. 
Birth,  number  of  young,  85. 
Birth  weight  of  lambs,  262. 
Bitch',  genital  organs  of,  32. 
Blending  inheritance,  135. 
Blue-gray  cattle,  247. 
Border  Leicester  sheep,  87. 
Boyd,  249. 

Breeding     prematurely     decreases 
size,  272. 


Breeding  season,  62. 

dioestrum,  55. 

metoestrum,  55. 

oestrum,  55. 

prooestrum,  54. 
Brooks,  134. 

Brown-Sequard  experiments,  208. 
Brull,  127. 
Burbank  method,  302. 

Calcium    in    rations   for   pregnant 

swine,  264. 
Castle,  194-294. 
Castration,  22. 

influences  secondary  sexual  char- 
acters, 186. 
Cattalo,  250. 
Cell,  1. 

contents,  4. 

division,  8,  9,  10,  11. 

germ,  2. 

growth,  7. 

structure,  4. 

theory,  the,  1. 

the  physiological  unit,  3. 
Cell  division  a  cause  of  variation, 

210. 

Characters  correlated  with  fertility, 
102. 

originate  in  germ-plasm,  195. 
Chillingham  cattle,  224. 
Chromatin,  6. 
Chromosomes,  12,  13,  135. 
Cole,  50. 

Color-blindness,  188. 
Community  breeding,  299. 
Connaway,  128. 
Contagious  abortion,  123. 

complement  fixation  test,  128. 

diagnosis  of,  127. 

treatment  of,  124. 


305 


306 


INDEX 


Continuous      and       discontinuous 

variations,  151. 
Controlling  sex,  189. 
Cornevin,  229. 

Corn  ration,  effect  on  foetus,  266. 
Cow,  reproductive  organs  of,  29. 
Cows,  exceptional  fertility  of,  107. 
Cross,  the    first,  an   improvement, 

247. 
Cross-breeding,  243. 

a  cause  of  variation,  248. 

advantages,  244. 

effect  on  breeding  powers,  244. 

influences  fertility,  105. 

permanent  results  from,  243. 

to  increase  fertility,  245. 

to  increase  size,  246. 

to  restore  constitution,  246. 
Crossing  and  heredity,  247. 

bison  and  cattle,  249. 

species,  249. 

Dalrymple,  125. 
Darbyshire,  149. 
Darwin,  52,  72,  90,  146,  198,  210, 

221,  223,  225,  285. 
Davenport,  E.,  100,  210. 
Decreased  size  from  early  breeding 

not  transmitted,  273. 
Development,  255. 
De  Vries,  152,  302. 
Diagnosis  of  contagious  abortion, 

127. 

Di-hybrids,  155. 
Disease,  179. 

acquired,  180. 

congenital,  181. 

predisposition,  181. 
Duration  of  lactation,  81. 

of  oestrum,  63. 

Early  maturity,  283. 

pregnancy,  influence  on  mother, 

274. 

Eckles,  122. 
Eward,  263. 
Ewart,  122,  168. 
Exercise,  effect  on  lactation,  83. 

favors  fertility,  111. 
Experiments  by  Mendel,  131. 


Factors  affecting  fertility,  100. 
Fallopian  tubes,  27. 

obstruction  of,  118. 
Fatness,  excessive,  unfavorable  to 

fertility,  99. 
Female  reproductive  organs,  24. 
Fertility,  85. 

characters  correlated  with,  102. 
confinement  unfavorable,  89. 
correlated  with  size,  86. 
domestication  increases,  87. 
duration  of  reproductive  period 

influences,  88. 
exceptional  in  cattle,  107. 
in  horses,  106. 
in  poultry,  112. 
in  sheep,  110. 

frequency  of  recurrenpe  of    oes- 
trum, 88. 
number  of  mammae  as  related  to, 

101. 

nutrition,  effect  of,  on,  98. 
Poland  China  breed,  92. 
relation  of  age  to,  91-93. 
relation  of  gestation  to,  87-88. 
Fertilization,  33. 

changes  in  ovum  resulting  from, 

36. 

nature  of,  34. 

First  cross  an  improvement,  247. 
Flushing  ewe,  99. 
Foetal  development    and   heredity, 

261. 
Foetus,  size  and  vigor  influenced  by 

ration,  266. 
Food     supply,     excessive,     causes 

sterility,  99. 
and  body  changes,  165. 
influence  of  restricted,  165. 
Free-martin,  129. 
Function,  improvement  in,  281. 
milking,  281. 

Galton,  102,  295. 
Gametic  purity,  141. 
Gentry,  234. 
Germ-cells,  2,  12. 

origin  of,  40. 
Germ-plasm,  161. 

origin  of  new  characters  in,  206. 


INDEX 


307 


Gestation,  66. 

causes  of  variation  in  period,  72. 

period  of,  69. 
Geyelin,  97. 
Goodale,  23,  187. 
Goodnight,  249. 
Graafiaa  follicles,  25. 
Grading,  244. 
Growth,  256. 

a  cell  function,  259. 

by  cell  division,  7. 

capacity  for,  257. 

development  of  foetus,  260. 

effect  of  climate,  271. 

factors  influencing,  257. 

impulse  strongest  in  youth,  256, 
260. 

influence  of  age,  271. 

influence  of  food  supply,  257. 

influenced    by   early   pregnancy, 
276. 

relation  of  lactation  to,  277. 

retarded,  permanency  of,  268. 

Hagadoorns,  292. 
Hallett,  147,  301. 
Hart,  64,  266. 
Heape,  42,  54. 
Heat  or  oestrum,  41. 

duration,  63. 

during  pregnancy,  60. 

effect  of  ration  on,  64. 

recurrence,  63. 
Helme,  75. 
Heredity,  131. 

and  development,  132. 

and  foetal  development,  261. 

and  sex,  183. 

and   variation  not   antagonistic, 
124. 

definitions,  132. 

kinds  of,  134. 
Hinny  hybrid,  252. 
Huish,  43. 
Humphrey,  64,  266. 
Huxley,  151. 
Hybrids,  249. 

cattle-bison,  249. 

cattle-zebu,  253. 

hinny,  252. 


Hybrids  —  Continued 
mule,  170-250. 
sheep-goat,  254. 
zebra-horse,  253. 

Immunity,  181. 
Improvement,  280. 

in  early  maturity,  283. 

in  function,  281. 

in  milking  function,  281. 

in  size,  280. 

in  speed,  284. 

in  tendency  to  lay  on  fat,  283. 

in  wool  production,  282. 
In-breeding,  217. 

advantages  claimed,  218. 

bad  results  from,  219. 

Berkshires,  234. 

cattle,  223. 

Darwin's  researches,  231. 

decreased  fertility  following,  220. 

definition,  217. 

dogs,  228. 

fixing  characters  by,  240. 

limits  of,  238. 

loss  of  vigor  from,  220. 

mice,  231. 

pigs,  226,  234. 

prepotency  of  in-bred  animals,  241. 

researches  of  Ritzema  Bos,  232. 

results  with  different  species,  242. 

selection  important,  238. 

sheep,  227. 

Wistar  institute  experiments,  233. 
Incubation,  fowls,  74. 
Inheritance,  131. 

alternative,  135. 

blending,  135. 

mendelian,  137. 

mosaic,  136. 

of  disease,  179. 

of  polled  character,  144. 
Insemination,  artificial,  42. 
Intoxication  of  male  parent,  effect 

on  offspring,  49. 
Iwanoff,  43. 

Kehrer,  75. 
Kempster,  97. 
Kulbs,  89. 


308 


INDEX 


Lactation,  80. 

duration,  81. 

effect  of  exercise  on,  83. 

habit,  82. 

heredity,  82. 

influence  of  climate,  83. 

mare  mule  that  secretes  milk,  83. 

OBstrum,  59. 

relation  of  food  supply  to,  82. 

unusual  lactation,  83. 
Lambs,  birth  weight  of,  262. 
Langer,  31.  - 
Law,  68,  117,  124. 

of  ancestral  heredity,  295. 

of  dominance,  139. 

of  segregation,  139. 
Lead  poisoning,  effect  on  male  germ- 
cells,  50. 
Lillie,  47. 
Lock,  133. 

Lord  Morton  mare,  167. 
Lovejoy,  59,  236. 

McCollum,  64,  266. 
MacFadyean,  124. 
Male  reproductive  organs,  19. 
Males,  milk  secretion  by,  28. 
Mammae,  number  as  related  to  fer- 

.tility,  101. 
Mammary  glands,  28,  81. 

milk  secretion  by  males,  28. 

milk  secretion  in,  31. 

structure  of,  30. 
Mare,  genital  organs,  26. / 
Marshall,  47,  53,  56,  96. 
Maturation' of  ovum,  13. 
Mendel,  136,  137,  138. 
Mendelian  method,  303. 
Metaphase  in  cell  division,  10. 
Miles,  200. 
Milk,  80. 

analysis  of  milk  from  mare  mule, 
82. 

secretion  by  males,  28. 

secretion  in  mammary  glands,  31. 
Mironoff,  42. 
Monohybrids,  155. 
Monsees^  72. 
Morgan,  184,  194. 
Mule  hybrid,  250. 


Mule  hybrid  —  Continued 

and  telegony,  170. 

mare  secreting  milk,  84. 
Mutation  theory,  154. 
Mutilations,  207. 

Nabours,  253.  » 

Nathusius,  72. 

Nature  and  nurture,  159. 

Nucleoli,  6. 

Nucleus,  5. 

Number  of  young  at  a  birth,  85. 

Nutrition  influences  fertility,  98. 

(Estrum,  41,  55. 

correlated  with  ovulation,  42. 

duration  of,  63. 

effect  of  ration  on,  64. 

influenced  by  lactation,  59. 

recurrence  of,  63. 
Origin  of  germ-cells,  46. 
Ovaries,  24. 

removal  of,  23. 
Oviparous  animals,  18. 
Ovum,  13. 

fertilization  of,  33. 

Parturition,  75. 

mal-presentation,  77. 

normal,  in  domestic  animals,  76, 

78. 
treatment  for  mal-presentations, 

79. 

Pearl,  96,  97,  103,  108. 
Pearson,  103. 
Pedigree,  294. 
Penycuik  experiments,  168. 
Poultry,  age  influences  fertility,  94. 
Practice  of  breeding,  280. 
Pregnancy,      early     influence     on 

mother,  274. 
heat  during,  60. 
indications  of,  66. 
physical  examination  for,  68. 
Pregnant      swine,      high      calcium 

rations  for,  264. 
Presence  and   absence    hypothesis, 

148. 

Previous  impregnation,  influence  of, 
174. 


INDEX 


309 


Primary  sexual  characters,  19. 
Prophase  in  cell  division,  8. 
Protein,  effect  of,  on  foetus,  266. 
Protoplasm,  1,  2,  4. 
Puberty,  56. 

conditions  influencing,  58. 
Pure  lines,  146,  291. 

Vilmorin's  wheat-breeding,  292. 

Ram,  age  influences  fertility,  94. 
Recurrence  of  oestrum,  63. 
Reduction,  37. 

chromosomes,  37. 

in  the  female,  40. 

in  the  male,  41. 

Registered  breeding  animals,  296. 
Registry  associations,  297. 
Reproduction,  16,  183. 
Reproductive  organs,  of  the  female, 
24. 

of  the  male,  19. 

Retarded  growth,   caused  by  pre- 
mature breeding,  274. 

permanent  effect  of,  268. 
Ritzema  Bos,  232. 
Rommel,  92. 
Roux,  38,  39. 

Secondary  sexual  characters,  19, 185. 
Selecting  the  best,  300. 
Selection,  284. 
aids  to,  288. 
importance    in   animal-breeding, 

286. 

methodical,  286. 
natural,  285. 
Sex,  183. 

effect  of  age  on  determination  of, 

189. 

effect  of  nutrition  on,  191. 
influenced  by  maturity  of  ovum, 

192. 

not  controlled  by  external  condi- 
tions, 194. 
proportion  influenced  by  season, 

193. 

Sex-linked  characters,  188. 
Sexual  glands,   transplantation   of, 

187. 
reproduction,  17. 


Sheep,  fertility  influenced  by  age, 

93. 

Size,  decreased  by  premature  breed- 
ing, 272. 

improvement  in,  280. 

of  litter  influenced  by  age,  91. 
Somato  plasm,  161. 
Sow,  genital  organs  of,  30. 

size  of  litter  influenced  by  age, 

91. 

Spallanzani,  43. 
Spaying,  23. 
Spencer,  71,  133,  167. 
Spermato genesis,  41. 
Spermatozoa,  14. 

vitality  within  female  generative 

organs,  46. 

Spermatozoon  in  fertilization,  37. 
Sperm-cells,  conditions   influencing 
vitality,  44. 

weakened  by  too  frequent  breed- 
ing, 45. 

Steenbock,  64,  266. 
Sterility,  113. 

abortion,  120,  123. 

causes,  114,  119. 

closure  of  cervix,  117. 

excessive  food  supply,  99. 

fatty  degeneration,  120. 

in  the  female,  117. 

in  the  male,  114. 

obstruction    in    Fallopian    tube, 
118. 

twin  births  (free-martin),  129. 
Stockard,  50. 
Superfoetation,  60. 

examples  of,  61. 

Tanner,  104,  116. 
Taylor,  126. 
Telegony,  166. 

possible     appearance     in     mule 

breeding,  170. 

Telophase  in  cell  division,  12. 
Tessier,  70,  72. 
Testicles,  20. 

Theory  of  pure  lines,  146. 
Thomson,  133. 
Thornton,  59. 
Thury,  192. 


310 


INDEX 


Transmission  of   acquired   charac- 
ters, 157. 

Transplanting  sexual  glands,  187. 
Triplet  calves,  108. 
Trowbridge,  P.  F.,  258,  268. 
Twins,  101. 

Union  of  egg  and  sperm,  36. 
Unit  characters,  141. 
Use  and  disuse  as  causes  of  modi- 
fications, 212. 
Uterus,  28. 

Variation,  195. 

among  cows,  203. 

causes,  210. 

continuous    and     discontinuous, 
150,  151. 

examples  of,  200. 

functional,  199. 

germinal,  214. 

infertility  of  animals,  200. 

meristic,  198. 

morphological,  196. 

physiological,  197. 

use  and  disuse,  212. 
Verworn,  1. 


Vilmorin's  pure  line  wheat-breeding, 

292. 

Virchow,  2. 

Viviparous  animals,  18. 
Von  Guiata,  231. 
Von  Siebold,  192. 

Waters,  257. 

Weismann,   34,  38,   39,    167,   207, 
210. 

and    Von    Guiata's    in-breeding 
experiments,  231. 

theory  of  reduction,  38. 
Wentworth,  81,  101,  107. 
Wheat-breeding,  147,  292. 
Wheat  ration,  263. 

effect  on  foetus,  263. 

effect  of  milk  secretion,  267. 
Wilsdorf,  230. 
Wilson,  8,  33,  36,  38. 
Wool  production,  improvement  in, 

282. 
Wright,  74,  246. 

Xenia,  176,  177. 
Zebra  hybrids,  168 


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